You know, something I always hear from theists is the claim that without god, there could be no objective moral standard. Why be good if Big Brother isn't watching? The question is why not be good anyways?
Today, after returning from my morning lecture, I parked in the pay lot to go up to my lab. The lot has an honor box where each space has a slot with the corresponding parking number. As I went up to pay, I noticed, as I often do, that one of the slots has the corner of two rolled up one dollar bills sticking out. Enough so that if I wanted to, I could have pulled them out, and used them to pay for my space. I immediately recognized, as anyone would, that this is a viable option. However, I was not compelled to do so. Why not? Was I worried that I would break a commandment, even though I might want to save $2? No.
As with all morality, I simply thought to myself as I walked away after paying for my space and pushing the other person's money safely in their slot, what if I had taken the money and that person's car had been towed? What if that was my money that had slid out after I was well into my day? I did what I did because I would hope that someone else would do the same for me. I wouldn't want that person to come out to find their car gone....I've been through that hassle myself. Once we realize that other people share the same experienced, the same pain, the same pleasure we do, morality should be obvious. Be good, for goodness' sake!