Atheism is a religion no different then the rest. It's impossible to *prove* that no higher powers exist for the same reason it's impossible to *prove* that they do. One can use anecdotal evidence or subjective opinion as a basis for either yet that doesn't constitute proof. In order for someone to be an atheist they must have faith and believe in the non-existence of any higher power, thus the absence of a higher power takes on the role of such a higher power. Furthermore other religions can at least state definitively what they believe in, atheists are incapable of stating definitively in what they believe in.
I mention that to liberal atheists and watch their heads explode.