I think you might be falling prey to a sort of fundamental attribution error for comments... thinking of all votes on a comment as being about the internal traits of the comment itself.

I generally vote to enact a total ordering on all current content, aiming to raise valuable/unique/informative/pro-social content to reader-serving prominence. This involves determining an ideal arrangement of content and voting everything down that is too high, and voting up everything that is too low... except, I try to keep the floor at zero total except where content is (sadly) above the sanity waterline of LW, as with some discussions of gender relations and politics.

About the only "pure knee jerk voting" I engage in is upvoting of content that isn't mind-killing in itself but that has a negative total. Sometimes I upvote a comment simply because someone said something really awesome as a rebuttal to it, and that comment/rebuttal pair is worth reading, and the way to give the conversation the order-of-reading-attention it deserves is to upvote the parent.