The ones against any kind of monetization at all are already vocal enough, let alone the people who would balk at anything that monetizes user data.
If you look at their change where they introduced affiliate link rewriting it's really surprising. They did it in a way that made sure they wouldn't affect any 3rd party apps, they gave everyone 2 ways to opt out, and didn't rewrite links that already had an affiliate code. And yet even with all of that, there was a ton of outcry and anger at the change.
Reddit as we know it won't be massively profitable, because the vocal users of reddit are so completely against any form of monetization.