Atheists, what do you mean by something being "good"?

This goes much deeper than the common atheist rallying cry: "you can be good without God." If the material world is all that exists, then the atheist and believer alike might *think* they are acting good, but "good" is without robust meaning. All that exists are preferences, pragmatics, and the herd morality. Upon what basis do you say racism or homophobia is wrong? Not wrong "for you," but wrong, period. What would you say to someone who comes from another culture who holds those things to be good? Is *anything* wrong universally (rape? murder? judging?), and if so, what are you prepared to do to enforce that morality? Why should someone be concerned, on atheism, about obeying the herd morality and following our evolutionary past, especially when he can get away with it and benefit from it personally?