You could make similar arguments about gambling being a moral panic and they shouldn’t ban that on the site. Selling sex to kids is just as exploitive and repugnant. Maybe selling violence to them is too. You’ll eventually find a line to draw for something being a vice, even if you don’t think this is it.
I think the fact that it is exploitive should ban it. I don’t particularly view twitch as the vanguard of a sexual revolution. I view it as a profit extracting arm of a megacorporation. It’s explicit selling sex to kids. It shouldn’t be normalized. You could argue that sex should be normalized, but exploitation (particularly in a sexual context) of children should not be.