Hypocrite – A person who engages in the same behaviors he condemns others for.
“One tries to wash away the taint that your opponents have attached to you by finding someone within your own movement who is more distasteful, more extreme, more socially maladroit, then denouncing him. Best of all if you can lead the chorus of ostracism. That renders you yourself ritually pure, at least for a while – and joins you securely to the community that has now been purged.”
Update: A good description of Ian Jobling too.