Why to not do bad things

Being nontheistic and awfully relativistic used to cause me to jump through all kinds of hoops to justify moral behavior. I have only casually come across an approach that, for me, skirts these issues nicely:
I've found that when I do things that I think are wrong I cause damage to myself, and that this damage is enough of a reason to stop such behavior (or reevaluate the violated moral).

By paying attention to my thought patterns (What are the things that you are thinking about when you don't realize that you are thinking? Where does you mind wander after this or that happens that you didn't realize it wandered?) has brought a striking idea to mind. I won't call it a hypothesis, because I know it works for me, the question is can it help you?

I'll start with an example: I bike recklessly. If you drive, I am one of those people you can't stand. I noticed that often, after running a light, I would, without thinking about it, start running through my head the imaginary conversation I would have with the cop who will one day, eventually, pull me over. I noticed that this coversation was little more than me weakly justifying the action to myself, and I was, in a sense, lying to myself. I recognized this as a form of damage that I was inflicting and that there were only two things I could do to stop the damage:
I could stop breaking the law.
I could stop accepting that its wrong to break the law.

The second sounds absurd, and in this case I don't feel that it was appropriate, but there are cases where it is more sensible. For example, people who are fat and depressed about it have only two things they can do to stop damaging themselves in this way:
Lose weight.
Stop thinking they should lose weight.

This isn't the full story, and I'm still experimenting and paying attention (and running lights and damaging myself and learning). But even in this state, it is useful perspective in my day-to-day self monitoring.

Here is a sketch of the process. When you do something that you think is bad (so, you see, I'm not talking about morality so much as social training) you enter self-critical thought patterns. These patterns are healthy if they lead to changes in behavior or policy (what you think is wrong). But if they don't lead to either, then constantly rehearsing these patterns strengthens them and ultimately affects mood and physical health. I've observed this. So: by doing things that you've agreed are bad, you are damaging yourself.

I'm not really a fan of the current gametheory/evolution/economics thinking that all cooperation and altruism is selfish, and this only incidentally fits in with that. Much of it comes from experience with Vipassana thought and meditation.