The stance — cultural, moral, or political — that sex, or particular practices like porn, kink or sex work, is inherently dangerous and suspect rather than a neutral part of being human.
Sex-negativity isn't prudishness with better PR. It's a whole worldview: sex gets treated as a special category of danger, guilty until proven innocent, something to be contained, licensed and apologized for. The rest of life gets the benefit of the doubt; sex gets the suspicion. Gayle Rubin's name for this, back in 1984, was exactly that — a culture that files sex under "destructive force" first and "thing humans do" a distant second.
The tell is the hierarchy. Rubin drew a "charmed circle": the sex that gets a pass (married, monogamous, private, vanilla, coupled, for love not money) and everything ranked below it — queer, kinky, group, paid, casual, for pleasure alone. Sex-negativity is the machinery that keeps that ranking feeling natural, so that one person's desire reads as "healthy" and another's as a problem to be managed. You don't have to be religious to run this software. Plenty of secular, even progressive, rooms run it too.
This one lands close to home, because our whole scene lives in the lower half of that circle. The label got sharpened in the feminist "sex wars" of the late '70s and '80s, when one camp went to war on porn, sex work and BDSM. Naming sex-negativity isn't about winning an argument at a party. It's about clocking the moment shame is being sold to you as safety — and choosing, on purpose, a different default.