You seem to forget the fact that on the internet anonymity makes us even bigger liars and assholes. Also that these are kids going through puberty and the like, not a tribe of super mellow and "rational" people.
Even beyond that, extremely personal attacks are rarely "constructive criticism". "This guy is super ugly" isn't going to be super helpful on a personal improvement level.
Negative feedback on a personal level also rarely works. This talk was about performance reviews, but it covers the criticisms of people's personality.
https://www.youtube.com/watch?v=bGkVM1B5NuI#t=1402
Even beyond that, extremely personal attacks are rarely "constructive criticism". "This guy is super ugly" isn't going to be super helpful on a personal improvement level.
Negative feedback on a personal level also rarely works. This talk was about performance reviews, but it covers the criticisms of people's personality. https://www.youtube.com/watch?v=bGkVM1B5NuI#t=1402