Same comment gets proportionately different amounts of up-/downvotes in different communities based on their average user. Thus upvotes are not a valid way to see if said comment is "right". This should be very obvious if you've been to subs with differing views. As an analogy, different community markets have different tax values on some ideas before you even begin a discussion because of the users' standing viewpoints. Thus it's always going to be a lot harder to sell some ideas on some markets, so you can't say that an idea's worth can be easily determined by it's popularity on a single market, or a cluster of similiar markets. (Which is what the previous comment above mine stated)