Th epost above got me thinking; I really don't think that morality has a lot to do with our beliefs or lack of them period.
I think there are two basics sorts of people ( and this isn't an original thought ): those who can envisage getting away with an immoral or illegal action, and those that can't envisage getting caught. I would imagine that the second group out number the first group in the prison population by some margin. But I can't see why either group would alter in ratio depending on belief. It is more likely that as atheists are more highly educated they are therefore, statistically, richer as a group and therefore less likely to turn to crime for income.
Criminals come in 2 groups as well

, those that are criminals due to circumstance, and those that are sociopaths and psychopaths .
We all, also, determine our own moral boundaries no matter how much we'd like to claim otherwise. The sheer numbers of divorced Christians shows this to be undeniable.
Personally I feel I am a very moral person but my own morality also allowed me to take drugs in the past even though it is illegal. It allows me to drive a rather fast V8 engined car above the speed limit in conditions I feel are safe ( i.e. never in built up areas ), and again this is illegal but within my moral perimeter.
I also feel our morality can be overdriven by more primal urges for things like sex especially when under the influence of drink or drugs, but I would maintain that we often, when younger, takes those substances ( subconciously or conciously ) for that very reason, so we will end up in bed with someone at the end of the night when our morals might have persuaded us not to if sober.
Our basic morals, or lack of them, is inate, and we all build on those to create our own moral boundaries. Reading posts on this thread we often like a justification for our moral boundaries so they don't sound inhuman or arbitrary. Religion can give you that justification, we can se on this forum that it is used to justify a morality that allows anti-homosexual discrimination whilst the same religion can also be used to bolster a morality entirely at odds with that. Humanism, built on the premis of respect for all human life, can't fall back on a written text, only on a set of philosophical statements.
It is actually quite hard to be a humanist, especially as I have zero respect for bigots and would quite happily discriminate agaisnt the discriminators

, that means I am not a good humanist, and my morals are as suspect as anyone else's and entirely my own like everyone else's.