text: Look up the "No True Scotsman" fallacy.
  The fallacy is used all the time by conservatives.
  If a Muslim kills someone, why s/he must be a terrorist.
  If a Christian kills someone, why s/he must be crazy. Because no true Christian has ever shot anybody. The Crusaders weren't "real" Christians, for example, using their logic. Neither were the participants in the Spanish Inquisition.
  See: Planned Parenthood shooter, where the entire El Paso County law enforcement establishment, from the moment the shooter was apprehended, has been bound and determined to show the guy as crazy, despite the fact the shooter provides as arguments standard pro-life rhetoric. They have an economic and philosophical self-interest.