The third cause of trolling is incompetence. If you disagree with
something, it’s easier to say “you suck” than to figure out and
explain exactly what you disagree with. You’re also safe that way
from refutation. In this respect trolling is a lot like graffiti.
Graffiti happens at the intersection of ambition and incompetence:
people want to make their mark on the world, but have no other way
to do it than literally making a mark on the world.