Why is it socially unacceptable for athiests to speak with certainty about their religious views?

Why is it that Christians can talk about God and be 100% certain about it, but atheists can't talk about how god doesn't exist and be 100% certain about it. When people say god isn't real as a fact, people will say they have no right to say that. Then what gives Christians the right to be certain about their views, but atheists can't even express their opinion without being public enemy number one? Isn't being certain about god existing or not existing on the same level? Why do Christians get special treatment? If someone raised their hand in cl and starting referencing the bible, no one would even think twice. But if someone did the opposite, it would cause an uproar.