A lot of people assume that because they have no fear of repercussions in the afterlife, that atheists are on the whole, lying, cheating, theiving, perhaps even violent sort who have no qualms about committing any and all things considered sinful or unlawful.
As an atheist, what keeps me walking the straight and narrow?
1) Fear of jail, and for those little things for which I would never get caught,
2) A sense of cosmic justice, karma or whatever you may call it. This is silly I know, but there is something in me (perhaps a remnant of my first 16 years of Catholic indoctrination) that stops me from being mean to people or committing petty theft for instance.
You can be an atheist and a good person.