I expect randos on the internet to act like trash (if for no other reason, a chunk of the people acting like 12 year olds really are 12).

I don't understand why the response from people that should know better is to act surprised at them, and feel justified in stooping to such low levels and pettiness themselves.

Well, I guess I can make guesses as to the "why," but none of them are answers that would let me sleep well at night if I were the one doing it. Maybe the sleep deprivation is why they're so cranky.