Perhaps they think that if they act like they have real knowledge, Christians will collapse and give up their faith in God under the power of the mighty atheist (who is lying). If they had bothered to do actual research instead of relying on people who use the profound academic principle called "Making Stuff Up", they wouldn't be humiliating themselves.
In addition to sharing bad information with like-minded fools, they love to watch videos. After all, if it's in a video and it agrees with their preconceptions, it must be true! One of the most popular videos in the "Bucket-Full-O-Lies" category is Zeitgeist. This infected beast has been put down several times before. But for those of you who didn't get the memo, here is a ten-minute video that cites real information, and not the outright lies of Zeitgeist.