A Christian is someone who follows Christ and obeys His teachings. If you don't do that, I wouldn't call you a Christian. Jesus said to love your enemies, not kill them or has them. Hitler doesn't qualify.
Discussion
what percentage of his teachings? do you trust the bible is accurate to his teachings? what about unwritten teachings?
were the crusades christian? all that killing? and if there was no killing would you be a muslim now?
Jesus said to love your enemies, not kill them. And that murder is wrong. So did those people obey His teachings? Can they REALLY be called His followers?
thats the point so if they had not done those killings you would now be muslim and not having this discussion
but on the teachings, loving your neighbor and submitting to another religion and invading horde is something else