Edit: Why downvotes? Idea of communism does not propose violence, Nazis and ISIS on the other hand do.
Heck, there were 2 world wars in which communists countries were only involved in the second, and only on the allies side. How many people were killed there, including civilians?
And let's not get started in the 18th-19th century history, before marxism was even invented...
War, murder and dictatorship are what they are -- they don't just belong to one single side of the political spectrum.
In Indonesia, for one example, nearly a million communist sympathizers were executed by right wingers (as were in Pinochet's Chile and elsewhere). This is an interesting watch: