If you are really interested in whether the left or the right produces more violence, I suggest you check out the FBI's Most Wanted Domestic Terrorist list.  Of the fourteen domestic terrorists on the list,  3 are Communists,  2 are Canadian Quebecois separatists, 2 are Earth Liberation Front, 1 is a Black Panther, 1 is New Africa, 1 is Puerto Rican FALN separatist, 1 is an anti-Vietnam War bomber, two with Hispanic names are wanted for airline hijacking and one has no group information at all.  Not a single right winger in the group.