Why are people so mean on the internet?

People who use the internet sometimes say things that people wouldn't dream of saying. Like one time, there was a report of a beautiful, young girl from my country named Michaela Harte who was killed on her honeymoon and I asked one time on the internet "Why would anyone want to kill a lovely girl like her?" and then this guy kept sending me messages like "Because she's ugly, the killers did the world a favor" and that she deserved to die.