An easy answer to a difficult question
There is a scene in Ricky Gervais' series AfterLife - which follows Tony after his wife passes away from cancer. A coworker asks Tony: "If you are an atheist, and you don't believe in an afterlife. If you don't believe in heaven and hell and all that, why don't you go around raping and murdering as much as you want" This question is of course, a pretty reasonable question to ask a coworker.
As a non-believer, one is often confronted with this question. It's also often accompanied with the vigor of someone applying the final blow - the questioner ready to penetrate one's stunned silence with 'gotcha!'
Gervais' character replies with what I think is the best answer to this type of question. He says, "I do. I do go around raping and murdering as much as I want which is not at all."
I think it's a very clever inversion. The question when posed seems to beg a sophisticated answer. You almost start reaching, even if you are not philosophically trained, to some rudimentary intuitions of meta-ethics. But perhaps, the simplest answer that is sufficient is to say "no, I don't need to believe in a God, or in heaven and hell, or afterlives to NOT go around raping and murdering people."
Of course, philosophers won't think of this answer as the answer because they have other concerns to bear, but to the ordinary people, Tony's answer is, I think, the best answer.