Certainly some are using their beliefs as an excuse to kill for other reasons, manipulating the fear of unwitting participants. As with any and every belief system though-out history, it will be manipulated by some to their own ends.
I agree that it is probable that the majority of perpetrators are behaving out of long-held beliefs though. Beliefs that need to be dismantled.
see video (Vampire Legend) at: http://www.pbs.org/topics/history/world-history/
And note in this PBS documentary how the local villagers sanctioned the fugitive's behavior and motives. Curious also how the old 'deviant' burial evidence in Britain and elsewhere imply these same practices have been going on for millennia throughout Europe. This suggests, given suitable context (as in Salem, US not that long ago), such 'unenlightened, uneducated PNG primitives' conditioned behavior could manifest anywhere at any time. /s
Warning to readers: the article contains pictures of crowds in villages watching as women accused of witchcraft are tortured before they get burned to death. It's shocking, disgusting, and disturbing.