Austin Cline has a really nice reply that points out the unintelligibility of this old ad hominem:
It is simply nonsensical to insist that people don’t believe in some particular god simply because they don’t want to be held accountable to that god. Do Christians disbelieve in Zeus because they don’t want to be held accountable to him? Do Muslims disbelieve in Kali because they don’t want to be held accountable to her? Of course not — that’s so patently absurd that Christians and Muslims would laugh if it were seriously suggested and they might even be offended.
Why, then, do so many Christians (and some Muslims) insist on saying much the same thing about others? I think that it might be a product of their own personal attitudes towards their religion. It’s a common feature of many people that they tend to assume that others are pretty much like themselves, at least in the most important things: same desires, same motivations, same fears, same hopes, etc. It’s not always an unreasonable assumption, but at times it can be. People need to learn how to place themselves in the shoes of the “Other,” a person who can have radically different desires, motives, fears, hopes, etc. while still being a decent human being.
I think that this attitude manifests itself in part when religious believers assume that atheism is a religion. After all, their beliefs are a religion and therefore anything that seems to take the place of them must also somehow be a religion. Perhaps something similar is occurring in the above: if a religious believer places their moral “accountability” in the center of their relationship with their god, then they might assume that others place a similar emphasis on being morally accountable. Why, then, don’t they believe in this god? Because they don’t want to be morally accountable — they want to be free to sin and do evil things without guilt.