I think you are missing the point of subreddits. They are not for finding people that agree with you, they are for creating communities with all kinds of opinions. I go to /r/fitness exactly because I don't share most of the ideas there. I go there to learn something new.
If I want to know everything that happens in the world of fitness, I subscribe to /r/fitness. With automatic recommendations (and without subscribing to /r/fitness) I'd never see stuff that I didn't know I was interested in.
That's the problem with automatic recommendations - paradoxically, you can't discover new interests with their help. You can discover what's happening inside your sphere of interests, but you can't discover new interests.