Why are atheists moral?

It’s a question which gets asked with a depressing frequency on theist blogs. The following is a comment by Alex, but it expresses a worry which seems to be felt by a number of religious believers:

My natural impulses strongly urge me to do things that most any reasonable person would admit is immoral. My immoral urges are often much stronger than what I know to be the moral action. I have the ability to choose which option I go with. I use reason to play out the scenarios of both choices before I act. If I am able to reason that I could go with the "immoral" impulse (that is much stronger) and get away with it, is there anything that should stop me from pursuing this end?

I to – being human – have a number of “immoral” urges. So why don’t I act on them? Hmmm… perhaps because doing so would more than likely leave me friendless, jobless, hunted by the police and wracked by guilt at the misery I’d caused.

At what point does that become attractive?

Immoral acts – i.e. acts which cause pain and/or suffering to others – are attractive only to psychopaths. The rest of us, regardless of our metaphysical beliefs, have plenty of good reasons – internal and external – for avoiding them.