I've often said that Athiests end up proving God's existence even when they're denying it. One more way they do this is shown in the way they attack the Christians but never the Muslims. Honestly, have you ever seen an Athiest try to argue with a Muslim? I doubt that they'd even be able to understand each other, what with all that silly yodeling in the Muslim language.
But remember that Athiests are dumb, and not being able to understand what their opponents are saying has never stopped them from arguing before. Just look at how idiots like Dick Dawkins and Christy Hitchens and Paul Maeyers attack the God without even looking at the sophisticated theological arguments that show how self-evident God is. So what's stopping Athiests from going after the Muslims?
God is, that's what. The Athiests know that the Muslims worship a false god named Alla, and since their god doesn't exist and hasn't written any morals on their hearts, which is why they're so quick to protest and attack and behead people. Christians, on the other hand, are restrained by the One True God, and so much as we might be tempted to, we can't go around cutting the heads off of every Athiest who makes us upset, or forcing all our women to dress in incredibly modest clothing, or cutting out our sister's sinful parts so they won't go whoring themselves out and making our fathers blame us for not being good examples of proper moral behavior.
If Athiests really didn't believe in God, then they'd be just as likely to go after Muslims as Christians. They don't, because they know that the Muslims would dismember them, and they know that the real God will prevent Christians from doing the same.