Atheism refers specifically to ones belief in god. A lot of people make the mistake of thinking that atheism means a total lack of faith or belief in anything. For example, Buddhism is an atheist religion; the two words do not cancel each other out. You can have beliefs and faith without thinking any sort of deity exists.
As an atheist I believe in fair treatment of everyone regardless of gender, race or sexual orientation. If this life is all we have, then it is even more important to live it well. If I just ran around breaking all the rules, I'd spend my one life in jail and would have wasted everything. Besides, I get satisfaction out of helping people or being kind to them, in much the same way I feel good when they are nice in return. I'm not saying I love public service, but even the best of us get frustrated now and again.
And, if you're wondering where these morals, or my conscience, comes from, I can only counter with; where don't they come from? Growing up our parents tell us not to hit our brother or we have to go to the corner. In school, the teacher tells us not to cheat on our test or we will fail. And in adulthood, the police tell us not to steal from a bank or we will go to jail. The concepts of right and wrong are so ingrained in our society that it's hard not to pick them up, regardless of religious affiliation. Perhaps some of these ideals came from religion at one point, but I would argue they are more a byproduct of community living and shared circumstance. We're stronger in packs so we must protect the pack at all costs. Hence; we will develop a system of morals that protects our mutual interests. Religion is just one method to bring order to a community and lay out ground rules. Some of us believe that it is no longer needed in our modern society, but that isn't true of all atheists. As I said before, one can be religious or have faith while not believing in god. But, thank you for asking the question. A great deal of people do not seek out answers from the opposing side.