A popular way to defend the indefensible, or otherwise to get around inconvenient counterexamples, is the "No True Scotsman" fallacy. In a nutshell, when you want to argue that no X would do an unpleasant act, and someone has the nerve to point out that Y, who is an X, did it, then you simply state that Y is not a true X.
Religious apologists, especially Christians, are masters of "No True Scotsman." When you point out behavior that identifies their religion as something other than all smiles and group hugs, they assert that no true member of their religion would exhibit such behavior. This leads to some interesting contradictions; for example, Catholics are Christians when people want to prove that America has an overwhelmingly Christian population, but not when anyone brings up the Inquisition.
Political apologists use it as well. For example, in the last century, apologists for communism argued that anything bad that happened in communist countries arose from the "fact" that those countries were using something other than true communism. More recently, a friend expressed concern over violence by someone identified as a leftist and said that no true leftist would do such a thing. When I explained "No True Scotsman" to him, he didn't budge, but said that even so, it was still the case that no true leftist would do such a thing.
Orthodox queer people also use it to dismiss any viewpoint diversity within the LGBT ranks. People have answered my disagreement with the party line by saying, "Yeah, but you're not really gay."