"Of course, not every atheist is a killer."
Nor is every theist, though you'll find a disproportionately higher number of theists have killed someone when compared to the number of atheists who have.
"Many atheists are afraid of the reaction of their theistic neighbors or they retain some shreds of decency from theistic parents or grandparents."
I don't even know most of my neighbors, theists or not, nor would I particularly give a damn what their reaction might be to anything that I might do.
Neither of my parents are religious in any way. When I was born I had only two surviving grandparents--one from each of my own parents--neither of whom were religious, or if they were never bothered to tell me about it.
"But, given free reign, how murderous could atheists become?"
Probably not very given that atheists recognize that society works better when we don't kill one another off left and right for petty reasons. Several theists quoted on this site, on the other hand, have outright stated that they would go on a murdering, raping, and pillaging spree were it not for their invisible friend keeping them in check. Which one seems scarier to you?
"Atheism is perhaps similar to anarchism."
Atheism has jack shit to do with anarchism, or any other "ism" you want to try to tack onto it.
"It may not explicitly advocate violence, however if widely accepted it does cause terrible destruction."
Cite your source for this claim.
