I've noticed that any time a debate of this sort comes up, and someone states a strong view supporting either side, the other side will start downvoting them. That's usually counteracted by their own side upvoting them back up.

It happens to everyone, so it annoys me when I see people complaining about it in every HN thread that has divided opinions on some social justice movement or whatever.

There's no "Please explain why you've chosen to up/down vote" pop up on HN, so no one really owes anyone an explanation for it either. That's just how things are.