although i certainly agree with the statement of capricorn being a dark sign- i do have some additional points you may wish to consider
i think the main reason for capricorn being the darkest sign- or dark in general is because of
drumroll
saturn
now you cant really have a planet that represents death, coldness, fear, negativity, skeletons, mortuary's, limitation, melancholy etc etc - BE the lord of a sign and not have that sign be drenched in its qualities
capricorn is of course, the sign saturn is the lord of (and in traditional astrology yes admittedly aquarius too, but aquarius has in modern astrology a co-ruler named uranus- and in vedic for example, aquarius is what is called the mooltrikona sign of saturn, meaning that when saturn is placed there its qualities will be expressed in a far more exalted way- highlighting the more desirable aspects of saturn, capricorn has none of this- it does not have a co-ruler nor is is an exalted position for saturn, it is for all intents and purposes, its domicile, and because of that it is a hardcore saturnian sign- displaying, being, representing ALL of saturn in the most SATURNIAN way)
so if you have the lord of that sign being such a dark dark planet, and you may or may not have read or even experienced yourself how saturns influence can impact ones life- or the lives of many- you can see that of course its own sign would also have those qualities and embody them in whichever extent it may be
so capricorn is dark because saturn is dark and saturn rules capricorn so dark plus dark is going to obviously equal extremely-very-very dark
so thats generally on why capricorn can be considered a dark sign- i think i just said and am about to use the word dark a repulsive amount of times- my apologies lol
but regarding the placements of planets in this sign and wether they do, and if so, HOW a placement can actually manifest and exhibit and show this darkness - i do have an interesting theory
if we look at a person and his natal positions, i have not found (and this is my own personal opinion that may be flawed but it is what i have experienced and found to be true in almost every case i have seen) when we look at the natal chart, and we see sun, mercury, mars, venus, saturn itself, north south node, uranus neptune pluto whichever asteroid or even ascendant in capricorn- i can say with confidence i have not seen the effects of the entire mind or psyche or personality of the person becoming inherently dark or cruel meaning, yes they may have their negative sides but inherently- when you get to the core- its never that cruel saturnian cold darkness- its never the darkness that is at the core of their actions/behaviour/thoughts/mind etcetera
usually the capricornian influence regarding the sun is more evidence of a cruel father/motherfigure- a difficulty of loving oneself, an ego that has been bruised and someone self-conscious of themselves for any reason whatsoever (usually though with the sun its with the father or fatherfigure- as we cannot forget that the sun is the father of saturn and he rejected him severely- so when the sun comes in his sign, it signifies something of the same nature happening in the natives life)
the capricornian influence regarding mercury would be far more noticable in the native's ability to manage/plan/communicate things- in a very serious and really saturnian cold and to-the-case matter
the venus in capricorn shows more the way the native loves and the partner of the native- usually someone older as saturn is the planet that rules time and generally older people- this would be a person that loves status and is serious and comitted to his/her partner and the partner may have some dark cruel things but not the native himself PER SE (again- my personal opinion)
now with mars its exalted in capricorn and that has a very good reason- i wont go in to it too far but lets just say when pure hard energy is combined with a highly intelligent practical solution-oriented LETS DO THIS- shiz gets done and fast as well!
as for the other planets- you get the point- it has its influences, but never have i seen that to make the person a sick dark horrible fear-worthy individual
now where the interesting part comes in is in two other cases
even if someone has ALL their planets in ...lets say gemini- the sign of pleasant comunication, fast light-hearted talks, social butterflies extraordinaires jumping here and there talk-talk-talking all the way.... or even libra- venus's sign of balance, equilibrium, diplomacy, understanding and rational- even if they have all their planets in those or other more gentle airy or watery signs BUT their moon or jupiter is in capricorn- and there is no comforting aspect or placement that can bring some relief to the moon or jupiter in any way- lets say the moon is alone in the 8th house in capricorn, and it is squared by pluto whilst saturn is debilitated in aries- well then no matter that its a gemini ascendant- with lovely planets in libra and cancer- STILL because of the moon and the moon alone- that person will be a very very dark and cruel and almost always twisted pathologically severely grim individual
same goes for jupiter- although IF the moon is not in capricorn- and no other planets are BUT jupiter- the effect is not as severe as with the moon- but still- it will have its consequences, jupiter is the planet of giving, of teaching, of happiness, of joy, of sharing, of how you relate to others on a spiritual level- everything you intend- from a higher persective is seen through this planet- when it is in capricorn- the intentions are not clear, the outside may seem fine, but the inner workings always play out and they can be extremely malicious and indeed, as you say here, dark.
this is again, my very personal opinion, i may be so wrong you are now sitting there wondering where this crazy person got this lol- but i have seen this many a times, personally with people i know myself and also through studying charts of people i know and dont know on astro.com database, and their respective wikipedia pages did come in handy as well lol
i have read many posts and articles about the moon in scorpio- and yes that is also not a very nice position- but there is something human in moon in scorpio- it is raw, emotional, it is manipulative, mean, stings and hurts- but more out of a sense of extreme self-protection of themselves, their psychology usually inflicted with some sort of painful experience that they do not want to trigger in any way again because the memory of the pain is unbearable- they are the way they are because they have been hurt themselves, sure ...it is extremely poisonous- but its filled with human emotion like inner pain, jealousy, obsession, hurt and deep inner psychological wounds- but still- it remains human, it remains something we can relate to and we can sometimes almost say we 'feel' their pain and confusion- , on the other sinister hand- capricorn is cruel and dark not because it has been hurt and now is self-protecting and turned to darkness for that protection, no, for capricorn the reason it is so scary is the cold, cutting rationale- it is restrictive, it despises any form of emotion, any form of human emotion- it is always at a distance, it never lets anyone in or shows anyone what is going on- it is not in it to protect themselves or their inner self, they are dark because it is what gets them the result they want- what they want to achieve- it can do the most horrible things and think it is doing the right thing because it will give them what they want, and achieving what they want has the highest possible importance- it will a give clear logical explanation and by that they stand and from that they operate- it is always self-serving and never takes in the impact other people may feel- because other people dont matter to them its not about the people, its about what i want to achieve (the mountain goat- it climbs alone, it is steep and it is dangerous but it goes ALONE and it will get there no matter who or what- emotions dont count on dangerous edges, getting to the top is what matters nothing else)
even looking at the rings saturn has- thats a physical barrier between him and the rest of the universe- no other planet has this- there is a clear wall between you and others- the coldness, the cruelness and the darkness are not as in scorpio- emotional, gripping, filled with anger and hot steaming intention (as mars is the very hot hot steaming planet- red with energy)- saturn is cold and slow and it takes time, it can wait, it can wait and never even blink- and thats whats scary and dark- is that its inhumane, its unbendable, you cant negotiate, its stubborn and it will do what it thinks is needed to get where it wants to be- and it is impossible to change their mind, for they will agree- in your face they will say yes so you wont bother them again- but they still will do what they want- and that inability to change- is what is truly horrendous, because you can use compassion, pleading, forgiving, loving, caring, asking, begging, hysterically crying or talking with a scorpio moon- it is possible to through deep waters get through to them- in having a human approach and understanding them and giving them that understanding they will feel a connection- but you cant do that with saturn- with capricorn- you just simply cannot do that- for they despise emotion, they do not WANT to feel connected to anyone- they dont CARE about crying and begging and loving- they have a goal- and if they decided you can cry for 6 years and believe me- its going to make them tired and bored of you- not compassionate and caring.
think about it, whats scarier, a hot-headed italian mobster that does shoot and kill and rages with pride and arrogance but still has love for their immediate family and kids and the honor not to kill woman or children (maybe bad example you get the point) - OR what is scarier the Hannibal Lector murderer-type that may have locked 3 woman in his basement and yet he goes to work every day pretending nothing is going on and silently doing what he does- no show of any remorse or guilt even when caught
this is a bit creepy- but if you got my main thought out of this thats the point- enough of the creepy examples lets go on with the emotions-
the lack of understanding and displaying human emotion- thats why it is a dark placement- its the aspect regarding human emotion that makes it this dark- they do have human emotion of course and its not like they dont understand it or dont 'get' why others do- the really really scary thing is they absolutely understand everything fully- they are not emotionally stupid- they get why- but it just doesnt matter to them, it plays no part in their consideration of anything- emotions are understood but that doesnt mean they are respected in any way- i think if you say the words human emotion to them they moon internally cringe- emotion is avoided and looked down upon- they cannot and dont want to see it in others- and you sure as hell will never see it coming out of them- as you may have noticed already if you know any cappie moons- emotion is not regarded as a critical and important aspect of human life- instead it is seen as a cancerous hiv-virus-like problem that has to be exterminated out of their system immediately and never to be spoken of again, it is something to be ashamed of, their true emotions will never ever come out- they would truly rather die
(not to say that they wont display emotion- but this is usually done in the knowledge that we like to see emotion in others and in order to achive a capricornian goal they will do everything it takes- and if that means to fake an emotion than of course they will do it- they are not a sign that you can say has integrity- if it needs to be done its going to be done- THATS how hardcore they are- even doing something they hate with pure white hate is still something they would do if it would bring them the desired result (and when i say do, i mean fake to the best of their ability because again, the real emotion will never ever see the light of day, but they can sort of use it to get some inspiration and then lie from that point on)
and just as a final statement, if we count the 10 planets (sun, moon, mercury, venus, mars, saturn, jupiter, uranus, neptune and pluto) i have 5 of them in capricorn- thats half- im one of capricorn-stellium kids, and i have been following a couple of threads online, reading about this cap-stellium, in contact with a few as well, and seeing them just living life in general- i wouldnt say these people (or myself) are dark per se, perseverance, ambition, education, goal-setting and getting, doing things alone and never stopping- yes- thats all true and its all capcornian- but never cruel or dark or in any way hurtful or not ethical- i have found almost always with a sense of integrity- but again, if i see someone like myself having sun, mercury, saturn neptune etc etc but NOT moon or jupiter- thats all true- but the second that moon is in capricorn- that changes, and it changes EVERTYHING- so i dont think having like myself and many other of those kids a LOT of planets in capricorn makes us dark- on the contrary- it makes us resilient- but again, if that moon or jupiter is there- no matter what else is going on in your chart- something dark is going on for sure for sure one thousand capricornian percent!!!