There are different kinds of not being into kink though. I very rarely meet a guy who doesn't enjoy kinky sex on some level. And some of the most kinky guys I know basically think people in M/s relationships are deluded and often dangerous. They are vanilla. They have vanilla relationships. They are just perverted and dominant in the bedroom. I also know some guys who identify as Dominant but aren't very kinky at all in the bedroom. They aren't vanilla though.
My point is that saying "he's not into kink"doesn't cover it. If I say to a friend that I meet a vanilla guy, they know it's going to be a blokey bloke who is dominant in the bedroom but they might not know if he identifies as a Dominant, which would give an indication as to what sort of relationship, I might develop with him. If I said "he isn't kinky", they'd ask how we are sexually compatible because they'd assume I mean he doesn't power play at all. Vanilla just sums it up quickly.
My comparison to monogamy was more about how some people in alternative lifestyles claim that their choice to go against the grain shows some sort of superior enlightenment.