Because that's all they're good at. Leftists have no actual talent; for this they hate themselves. They see other folks, who do have talent. This makes the leftists jealous, and they hate the talented folks as well.
I have said for years that leftists lie all the time. I should add that leftists hate all the time, as well.
And this is appropriate: leftists re-make themselves in the image of their master, who was a liar (and a hater) from the beginning.
There are also plenty of talented leftists, to them it is all about being cool, fitting in with their crowd and being part of their perceived status quo.
talented losers...
Sometimes, there are things that need to be destroyed - Jim Crow laws come immediately to mind. But generally, their appetite for destruction is limitless and is turned randomly on whatever happens to be in their way. And, when they run out of "enemies", they'll turn on themselves (which is where we are, in part, today).