Why are people always being rude to others when they write mean comments on their posts

I think some people feel free from societal constraint online. So stuff they would never say (due to jealousy, petty anger, etc) they say online because its easy to not stand behind the things you say on the internet. It is easy to distance yourself from your words and forget about the things you have said in the next second. Simply speaking I don't think people always really mean what they say its just that they can say it.