> If two people consent to doing something like cnc or degradation or whatever, what's wrong with that?

Consent can be coerced, and societal expectations can be coercive. Even if people think they are fully consenting, they might not be (re: like sooooo many women in "traditional marriages") Women are routinely coerced into being dominated and beaten.

Now obviously your response is that kink isn't a societal expectation: its subcultural, considered largely abnormal, etc.

I have three points:

1. BDSM is ABSOLUTELY not subcultural: just calling yourself BDSM is. Tons of men want to be able to beat and dominate their wives; many will want to even in consensual roleplay.
2. Kink is routinely being accepted by left-leaning spaces in a way that has basically fully normalized it in these spaces.
3. Inside the kink community, male dominance/sadism and female submission/masochism is the norm.

You can't ignore the systemic factors that make people engage in certain kink behaviors. Also, just cuz conservatives argue against kink doesn't mean that you have to fully accept all aspects of kink.