The idea that only religious people have any interest in moral behavior is completely wrong-headed. It's quite easy -- for someone who bothers to reason it out -- to come to the conclusion that moral behavior is in your own self interest. In other words, it's pretty easy to argue that moral behavior optimizes your own world experience. Read the following carefully, it's simple, but requires thought.

Here we go:

No man is an island (well, no person is, but why mangle the quote). There are only a few general sources of pleasure in our lives. We have the pleasure of our own thoughts, the pleasure of interacting with our friends and families, and the pleasure we take in experiencing the material world (skiing, listening to music, playing a game, watching movies, taking walks in the park - whatever your thing is). My experience is that my own thoughts are easier to live with if I've followed the straight and narrow, but perhaps there are people who enjoy being bad, so we'll assume that, within your mind, you can enjoy yourself whether you're a good person or not. If you're an immoral jerk, however, you aren't likely to have a pleasant time with your friends and family. If you're immoral enough, they probably won't want to have anything to do with you. Similarly, the pleasures of the material world are highly dependent on the good works of others. No one makes soccer balls, you can't play soccer. No pizza place, no pizza. No grocery store, bummer, you get only the food you can scrounge on your own. No one feels like making music, you can't play any CD's. No one invents the air conditioner, you sweat. In other words, any pleasure you're going to take out of your interaction with the material world is heavily dependent on the rest of humanity doing their thing as effectively as possible.

So, big chunks of the pleasure you can experience in life are dependent on the people around you. If you want to optimize the pleasure you take out of life in a totally selfish way, your best bet is to make sure that you aren't a jerk to the people around you and that you do everything you can to make them as productive as possible; because the fruits of their productivity are all potential sources of fun for you. The better the rest of the humans in the world are at making good music, writing good books, producing good food, thinking up neat things to do and generally enhancing the world, the better your life will be. The one thing that you personally can do to make them more happy and productive is to make sure they're safe from all forms of attack: from harsh words or financial cheating to adultry or murder.

This doesn't mean you should give all your belongings to the poor. You can, of course, and it might do some good, but what really makes people feel good (at least in my experience) is to be given the chance to go out and do their own good stuff and find their comfortable niche in the world. They want to make their own contribution to the big picture. This means supporting governments and society that promote freedom and the rule of law.

"Ah", I hear you say, "surely I can cheat a few people. No one will know if I just steal a little from people who won't miss it or fool around with just one other person's spouse. I don't have to be moral all the time." My answer would be, yes, you do; if you really want to optimize your life. Sure, you might steal a candy bar the next time you're at the store and no one might notice it. But what if they do? The minor pleasure that you might get out of that candy bar is offset by the minor chance that you're either caught (and pay a penalty) or that you cause someone else to catch hell for not stopping more shoplifting or that the actions of many people like yourself put the store out of business. Your small pleasure will contribute in a small way to events that might cause you to have less pleasure in the future. Think about those neighborhoods where shoplifting is so bad that no stores will come there or the ones that do charge a lot more: no one may have taken a LOT, but collectively their immoral behavior has made their lives less pleasant.

So, even if your motives are completely selfish (the opposite of the roots of religious morality), your best move for optimizing your experience in the world is to live a moral life. QED.