You are supposed to upvote things that:

• you like
• belong in the community it’s posted in
• upvoting favors it for the algorithm, ranking it higher and making it stay longer. If you want others to see the stuff, you upvote.

With comments, you are supposed to upvote things that contribute to the discussion, even if you disagree with it, but in practice people often just upvote what they like and agree with and downvote what they don’t agree with and there is pretty much nothing anyone can do to change that. So do what you think is right.