I'd wager you are correct that if it were required, nobody would comment on it except existing Reddit users familiar with their more privacy-respecting leanings

I'd wager you are correct that if it were required, nobody would comment on it except existing Reddit users familiar with their more privacy-respecting leanings from their past (ie. not new users). The dark pattern is that there is zero indicator that it is actually optional and they appear to go out of their way to hide that fact. It is about being upfront with your intentions, and what you are offering users.