Completely serious. Just realise that different people have different goals and/or different models of the world.

Downvote is merely a signal for "some people here don't like this". If you care about opinions of LW readers, and you want to be liked by them, then downvotes hurt. Otherwise, they don't.

For some sick person, making other people unhappy may be inherently desirable, and downvotes are an evidence they succeeded. Imagine some kind of psychopath that derives pleasure from frustrating strangers on internet. (Some people suggest that this actually explains a lot of internet trolling.) Or someone may model typical LW users -- or, in other forum, typical users of the forum X -- as their enemies whose opinions have to be opposed, and downvotes are an evidence that they succeeded to write an "inconvenient truth". Imagine a crackpot, or a heavily mindkilled person. Or a spammer.