So what?
"Someone" is integral to many movements, religous, politicial or otherwise. It shouldn't affect a person's ability to call them anything they want. You should argue against them with reason if you disagree, not due to some sort of protected status and certainly not with a lazy labelling of some sort of "ism" du jour.
I may think Stalin was a terrorist, but that doesn't mean I harbour ill-will to all Communists.