While not a practicing Christian myself, I must say I'm surprised and not a little dismayed that you haven't yet been taken to task for implying by your analogy that white supremacism is in any way an extension of Christianity in the same sense that militant Islam is an extension of mainstream Islamic thought; it's just not on the same spectrum at all.  There's nothing inherently 'white' about Christian teachings or belief.  So why should Christians specifically be called upon to disavow white supremacists in the population?