I feel like people downvote like that when they don’t like how the comment makes them feel, but can’t be bothered to think about why that’s the case.

And I have no interest in what those people think feel.

Alternatively, it can make me do a double take, and reconsider my own reasoning, just to make sure I haven’t made an error, in fact or in judgment. I don’t think you need to do that here; what the adult said was most definitely a potential threat.