Since we're not constraining ourselves to something like symbolic logic here, we should only be looking at good arguments on all sides that are not easily refuted. There should be good arguments that lead to interesting discussion involving conflicting arguments that are also good. For bonus points, there can be references or links to additional material, or the comment can even be well-written.

If the comment inspires a response at all, you should probably upvote it. If you want to respond and downvote it, you should probably either reconsider downvoting it, or consider that the comment was merely a troll, in which case you should downvote it and not respond.