I enter this topic cautiously and I am not wearing anything...flammable, that is. So, here goes:
byjove: Mars in the 12th is a placement that many very inspired people have. David Bowie and Camille Paglia for two off the top of my head. Mars in the 12th (natally) destroys your enemies and makes your a defender of whatever cause you find important or are inspired with. The 12 house alone (natally) is very misunderstood but...that is another thread someday.
OK, on topic: What I find most harmful to astrology, any type of any generation, is that there are a plethora of people with little understanding (or information) as to WHY it exists or came about.
For example, different house systems exist because those astrologers who were also highly skilled mathematicians and astronomers were evolving some then less accurate method of calculation that existed in their day.
Another reason was religious. For example, one reason William Lilly adhered to Regiomontanus was because he was Protestant. The Catholics did not like or use Regio, at the time and generally adhered to Placidus which, is really one of the main reasons Placidus became so popular.
Also, some systems are specific to a certain "flavor" or type of astrology and cannot be mixed and matched so easily. For example, as drfarr pointed out, Vedic used equal house system along with a few other ancients. BUT, now here is the BUT, generally, the rules for interpreting the chart are ALSO different. SO, you have a matched pair - a house system with a specific method or approach to the chart. You take one from anther and it begins to break down somewhat, like a fish out of water, so to speak.
House systems were later developed as ways to accurately and astronomically reflect what was seen in the heavens and how it was to be divided fairly at extreme latitudes. That's it! It is no more metaphysical than that!
At the risk of being lengthy (too late!) I agree with jmerle179 above who said something to the effect that as a newbie all this was too much and didn't help the skeptics either. I AGREE! Astrologers, as a whole, really need to unite on (and study) the theories and history of a method, rather than argue their preferences of a method and leave it at that. When in doubt, pick a master astrologer (historically), study their method, use their house system, and see if you can prove the results practically.
::Soap box discarded::
Blessings,
Anachiel
P.S. There is also a difference between a sign and a house, it seems obvious but, it is really an overlooked fact. One does not equate to the other. So, in essence, an intercepted house is irrelevant, truly. All the signs and houses are still there. It is simply the matter of proportion that has changed. Oh gawd, now someone will go off and write a book saying the size of a house is the amount of something that you have.....::grumble::