Karma is a reflection of someone’s engagement across multiple subs and multiple formats (comments, posts etc). It doesn’t reflect an opinion, it’s sort of a credit rating. Subs like dank memes put a lower bound as a credit check so that the mods aren’t flooded with bot posts.

Generally most posts are positively voted posts, albeit small. While some people may get downvoted for opinions, I would argue most things get downvoted for being inappropriate in nature rather than content. There are subs where unpopular opinions are upvoted.

In short, karma is social credit, not censorship, and downvotes are for inappropriate behaviour, not opinions.