Sex "It is because (this sort of?) sex is inherently violating, objectifying, manipulating. Consider: it is usually the man who asks for consent of the woman (to do things to her body, to use her body as a mean for his own climax, to satisfy some urge that is inherently questionable)."
Hmmm, I agree with quite a bit of what you say, but you also jump to conclusions and miss a lot of nuance. The issue of consent is actually quite simple. We ask for consent because it takes two to tango. The rules of sex are that it is intercourse with consent of both parties. If it is without consent it would be rape. Rape is a kind of sex frowned upon because sex against the will of one party is a very painful humiliating and unpleasant affair for one of the parties. So basically we require consent. I do not think it has anything to do with teh capitalust system. Sex is not 'inherently wrong', sex without consent is inherently wrong, much the same as violence is inerently wrong.
During the sex act you indeed use the other person for your pleasure, I agree with that. However the beauty of it is that the other uses you for that very same purpose. It is the mutual objectification that makes it moral. If objectification is merely one sided, yes than you have a point, but it is not. The point of it is, at least for me, that the other consents to the defilement, the base urges and what have you, but also has the right to use you in likewise manner.... and you even like it when he/she does... So yes, sex is most intimately bound up with consent, because otherwise the objectfication is just base and nother else than structural dominance in the worst form.