Sex is quite toxic; why wouldn't it be perceived as toxic? Sex, alone, has been the product of hundreds of thousands of deaths in the past few centuries. The effects of aids, HIV, and chlamydia are things anyone should fear. There is a justified reason why our minds have evolved to be monogamous. There may have been moments in history where entire populations were wiped out due to such diseases.
But it's rather funny; ironically, it's also very clean. Sex is the means we reproduce. You, me, we wouldn't be here if that wasn't the case. It becomes rather complicated because of this. However, much like germs, society and our own genetics favoured people who were more cleanse. Look at the Black Plague. That was considered the end of the world for most. There wasn't going to be a Europe after that. The ones that practise safe, hygienic practises survived; those who didn't died (to put it simply). The majority of the population loves sex, but they also consider it dirty, and this has been the better perspective to take on the subject and has been the most successful in society.
I think it's quite reasonable why we naturally think sex to be a rather "toxic" - as you put it - discussion.
When you try to take a rather complicated issue and simplify it, you can't come to a definitive statement on the majority of subjects. Not even sex. Hell, the emotion, anger, isn't a bad thing either yet we consider it to be.
Think of equality. You start speaking about that as much as we love to value everyone to be the same, the reality of the situation is that it becomes really complicated and we're not equal and we don't want to be. "We want equal opportunities, not equal outcomes. It's dangerous to have equal outcomes." And this is speaking as someone with an Aqua moon...
In saying that, the topic will evolve and evolve to the point you have 500 page textbooks on the subject matter that still evolves in time.
At the end of the day, it's what can be practically applied that makes the most significance. Keep sex as being considered dirty; because, frankly, we don't want everyone running around getting AIDs. But, keep it enjoyable so we can reproduce.