After doing some research I have come up with a few reasons that people behave negatively to one another over the internet, here is what I have concluded:
1.Many people believe that by having anonymity that they are free from reprimand in real life by their words they post.
2.Many come from harsh lives in the tangible world, so they use the internet as an outlet for their aggression that they bottle up in hide in the real world. (See reason 1.)
3.We as a species that love to argue and start conflict.
4. Many believe that they do not have to show common decency while on the net.
5.There are people who are over opinionated due to the fact in real life they feel they have very little say on what goes around them, so they take this out on people they meet online. (See reason 2 for. )
6.Some people like just like to stroke their own egos.
7.There could be a "wolf pack" mentality that you must support the various factions on different sites. If the new person or a person who does not see eye to eye with the group, you are to bash on this person to feel secure within this group.