Edit: Why downvotes? Idea of communism does not propose violence, Nazis and ISIS on the other hand do.
More people have been killed in pragmatic endeavours, like colonialism, and land grab/turf wars, than from "utopias".
This includes smaller scale utopias -- far less innocent people have been killed by ...hippies than by policemen.
Well, why single them out then if both sides can be dangerous?
If you think they are the "more dangerous", then I think the previous 2 milenia of bloodshed for pragmatic land/power grabbing, including WW I, refute that.
Besides, even so-called utopians are quite pragmatic in their actions. When Mao executed tons of people, it wasn't some "utopianism" guiding him, but a very pragmatic power grab to stay in power and get rid of possible contenders.
(You might say that this was only possible because his subordinates were deluded by some utopian zeal. But lots of other cases, from the Belgian colonies and Pinochet to Indonesian "death squads", prove that you don't need that to have mass killings, just unquestioned power and the upper hand).
>Did you reply this way because you approve of communism?
No, I replied this way because I approve of utopias. The US was one too at some point -- for persecuted from Europe religious nuts.
Also because I like being objective, which needs taking all sides into account. Of any binary (utopia/pragmatism e.g.) I'd never say "the first is dangerous" if the second has been historically proved just as dangerous.