It is asked what motives has an atheist for doing right. He can have the motive of pleasing himself and his fellow-creatures; of living happily and tranquilly; of making himself loved and respected by men, whose existence and whose dispositions are better known than those of a being impossible to understand.
Can he who fears not the Gods, fear anything? He can fear men, their contempt, their disrespect, and the punishments which the laws inflict; finally, he can fear himself; he can be afraid of the remorse that all those experience whose conscience reproaches them for having deserved the hatred of their fellow-beings. Conscience is the inward testimony which we render to ourselves for having acted in such a manner as to deserve the esteem or the censure of those with whom we associate. This conscience is based upon the knowledge which we have of men, and of the sentiments which our actions must awaken in them. A religious person’s conscience persuades him that he has pleased or displeased his God, of whom he has no idea, and whose obscure and doubtful intentions are explained to him only by suspicious men, who know no more of the essence of Divinity than he does, and who do not agree upon what can please or displease God. In a word, the conscience of a credulous man is guided by men whose own conscience is in error, or whose interest extinguishes intelligence.
This is one of my all-time favorites of Meslier’s arguments. If we grant man limited ability to know the will of god, which we must since men disagree and make mistakes, then it’s impossible for a person to know that they are doing right or wrong in god’s eyes – barring the notable exceptions in the various versions of the ten commandments. Indeed, even the transcriptionists of the ten commandments couldn’t know what god thought was right or wrong, because they’re different between Exodus 20 and Deuteronomy 5 – and different, still, from Cecil B. DeMille’s version that most Americans mistake for canon.
Given that people who believe they are following a divine morality are almost certainly mistaken to some degree or another, the atheist actually has to think about what is right and wrong, to them. And when the atheist transgresses, they are transgressing against their own values, their own decisions. As a moral nihilist I’ve long felt that it’s actually the most honest path: you must acknowledge that there is no reason to hold the values that you do, other than that you have chosen them – betraying them means violating your own world-view, or believing nothing at all. Note, I do not use the word “nihilist” to mean “someone with no beliefs” but rather “someone who is unconvinced of the basis for belief.” In that sense, our beliefs are our opinions and that makes mine extra-important to me, though I can’t blame you if you think they’re silly.
Meanwhile, the religious person has to confront and cope with the stream of contradictory and flatly immoral views promoted by faith, and has no ability to defend their opinions at all; they point a finger at god and say “what he said.” Which is sad because god hasn’t said anything for a very long time, if ever.