Yes, there is a dark side to atheist culture, and it may be the lack of culture. It may be that people have not figured out a way to teach young people to be moral outside of religion. Many young atheists of my acquaintance have no scruples about lying, cheating, stealing and stabbing coworkers in the back, but Christians, Muslims, Jews and Hindus all believe somebody is watching. Somebody sees everything. There is a kind of shock buffer to keep us behaving as we live out our younger years. As I've mentioned before I already know of two people who converted to evangelical Christianity that grew up secular, and I mean they converted knowing full well that they were joining a cult more or less. They joined because to them there was something wrong with secular culture. They chose to believe and to pass on their beliefs.