We already have people taking downvoting as a slight and demanding explanation;

Do we have that? It seems that we more have people confused about why a remark was downvoted and wanting to understand the logic.

That scenario has less potential for conflict, but it still creates a social obligation for me to do work that I didn't mean to volunteer for.

I don't want to deal with someone demanding that I, specifically, explain why their post is bad, especially not when the downvote was barely given any thought to begin with and the topic doesn't interest me, which is the usual case with downvoting.

That suggests that your downvotes don't mean much, and might even be not helpful for the signal/noise ratio of the karma system. If you generally downvote when you haven't given much thought to the matter what is causing you to downvote?

I meant, not much thought relative to the amount required to write a good comment on the topic, which is on the order of 5-10 minutes minimum if the topic is simple, longer if it's complex. On the other hand, I can often detect confusion, motivated cognition, repetition of a misunderstanding I've seen before, and other downvote-worthy flaws on a single read-through, which takes on the order of 30 seconds.