An atheist can be everything a theist can be, EXCEPT empowered by god, and a physical connection to god. (unless god decides to empower them anyway)
That is (in my experience) a huge limitation on an individual's human potential and ability. But those who chose not to believe are rarely given the opportunity to experience this empowement and enhancement, and so have nothing to compare their life as an atheist with. However wonderful and great a life is as an individual being, body and mind, it is better connected to god.