Why are religious people so afraid of Atheists? 
Because atheism is a sin and atheist sinners (2nd commandement).
Atheism is replacing G-d with an idol and idolatry is a capital punishment for 2nd commandement.
So being an atheist is worse than murdering/raping/escrow scamming?
Mind you, I can see why religious people aren't afraid of murderers - they are the ones doing all the killing.
Not worse in the direct comparison. However, atheism has no written direction to NOT do all the bad things. But most religion has some direction and directives against doing the bad things. Even Islam, with its directives to do violence, has directives for peace. Atheism doesn't have such, except on a personal level in some instances.
So the argument is without "God" humans would have no moral compass?
Well, if we make AI for real someday, the only place it will get morals is from people, right? I mean, it is very difficult, although not impossible, to figure out morals without instructions.
God made us, the AI. He implanted morals into us, and all of nature. But He also gave a form of free will.
