Atheist moral code

[CapnAwesome]

One key argument used by atheist to undermine religions is that many of them has books that clearly justifies rape, manslaughter and several other things that must be fundamentally evil.
In many cases this argument does not hit as hard as it should against individual believers, because they have found ways to interpret the scruptures so that these passages have other meanings, and the evil acts are not part of the individual belief.
When atheists attack these believers based on bad morals I sometimes feel like they are throwing dirt in their own eyes. Having no morals is not necessarily better then having bad morals. As far as I understand, atheism is based on a disbelief of gods, which don't automatically point in the direction of a moral code.
So, I'm wondering if there is some kind of moral code that all atheists would be bound by, which could justify these arguments. And if there is, where is it derived from?

Well some people believe there is a kind of natural morality. Think about this: at any given time and at any given decision there are outcomes that will either make the world better or make the world worse. If are faced with the choice of eating cupcakes or eating shit you don't say 'Well taste in food is a subjective thing, so it doesn't really matter whether or not I eat shit or eat cupcakes.' Of course that's not true, there is a right decision there and a wrong one. The same applies to moral decisions. If you are deciding whether or not to yell at your spouse or beat your kids, it's not a matter of subjectivity. There is a correct moral decision which brings more happiness to everyone involved. So there could very well be a moral code that derives from natural law. It's also important to separate from what people perceive as moral and what actually is moral. Even if a whole society says that it's okay to beat your wife and kids, it doesn't mean that beating your wife and kids is moral. All it does is add suffering to the world and doesn't result in anything positive. Even the one doing the beating is made to be less of a human and suffers for it.

Keep in mind, I'm only saying that there could very well be. I myself am a Nihilist, so I don't really think it matters whether or not there are morals.