I'm really sorry to hear that your stuff was taken. I don't know what makes people act that way. I really try to keep the bare minimum in the backpack that I carry. The most expensive thing is my swiss army knife.
I tend to keep my wallet, ID and other valuables all locked up in my car. The remote car key gets tied up inside my tent, so it just won't get misplaced.
I know you just wanted to get your annoyance off your chest, but planning for the worst senario in the future will go a long way.
Yes, karma is a bitch, and I hope the person that stole your stuff gets a non-curable rash in their groinal area.