it's becuase the internets is a place where you can say things without having to worry about consequences, and trolling is generally accepted so you can say things you'd never say in real life.
for example, you know a black guy is on a forum, you can say "shut up you stupid
****" cause it's the internet and it doesn't reallym atter, you will never see these people, same with telling a jew "you guys made up the holocaust" and the mask stuff,if they know you like him, just for the sake of a few laughs, you'll get the "stupid
**** deserved it" stuff. just gotta let it all roll off you, cause 99 % of the things people say they'd never say to someoens face