On what basis do you accuse Karadzic of mass murder?
It's their favorite cliche. One could accuse just about any head of state or government of that. Like the IRA could accuse british PMs of similar crimes. One could accuse Alija Izetbegovic of it, Franjo Tudjman, almost anyone on whose watch the state killed someone.
You have to understand that some people just blabber cliches because they can't come up with an original thought.