But there's a difference. Yes, horrible things have been done in the "name" of Christianity, but that doesn't mean they were ordained by God. Even if Hitler did say he was doing what he did in the name of Christ, that didn't make him a Christian. In the bible, the Israelites walked around and wiped out entire races in the name of God, because He told them to. I know it sounds hypocritical, but that's just the way it is.
Also, I am in no way saying that you can't be a Christian if you sin. We all sin. The only difference is, if you are a Christian, and you ask for God's forgiveness, and you are sincere, he will forgive you.
Finally, I am also not saying that Christians are the only ones who can do good things, but at the end of the day, your salvation isn't measure by works.