I think part of it is the anonymity of the internet. There is a perverse pleasure in vanquishing a foe in a game or in a forum. That very anonymity allows people to head for the dumpster immediately, and say things they would never say to someone in person.
I believe liberals must exist as a counterbalance to uncontrolled hard right thought, just as I also believe the opposite.
I would liken the effect to that of internet porn. Back in the day, seedy stores in seedy neighborhoods sold hardcore porn; now, with the internet, over 30% of internet hits/searches are for porn. It is anonymous, and even free (well, if you don’t mind viruses). Perhaps less anonymity, a sort of digital thing like the guy I saw on TV who couldn’t stop an ‘adult’ (Shakespeare?) book store going in. He resolved to toot his horn and wave anytime he saw anyone going in as he drove by at night.