Power hungry F'ers
Pretty much all Idealogies can be abused, except Nazism, which was used quite successfully to kill Jews.
Papists are an example of an abused idealogy.
I hear in southern France they have a (Catholic) ceremony where they parade the sopposed skull of the Mary Magdelene. Being an agnostic from a Protestant country, I find this ostentatious show of death worship quite disgusting. I'm pretty sure jesus didn't mean us to worship the mouldy 2000-year old skull of a prostitute.