What I've come to realize (despite avoiding such a negative conclusion) is that the dominant culture's experience with sex seems to be mostly limited to that which includes problematic power dynamics (e.g. mainstream porn, captive housewives as an ideal). They do not have a solid concept of consent. Sex is shameful to them because their concept of sex is, literally, shameful and exploitation is at the core of it.

Concrete and overt examples being unable to imagine someone being sexually liberated, a woman, and a feminist all at the same time (they see sex as inherently demeaning to women), or seeing male sexual success on a "nice guy virgin" (unsuccessful through insufficient exploitation) or "man-slut womanizer" (success through excessive exploitation) spectrum. (Even the word "womanizer" bakes this assumption in, to be made a woman, woman-ized, is to be exploited?)

It appears in popular discourse around trans individuals (choosing to present as a woman means you must have a sexual fantasy about being exploited, we can't expose that idea to children). Around homosexuality (so which one of you is the exploitative one). And around polyamory (you must have a cuckold kink because nobody would let someone exploit their partner otherwise).

But this same dynamic also appears in a more subtle form in daily interactions in the culture and shuts down sexual topics or behavior. It's somewhat analogous to the situation of shushing a white toddler that points out the race of a non-white person because it's "rude" - you've made it apparent that you think non-whiteness is something inherently uncomfortable for a non-white person to have pointed out so you try to "spare" them this.