[Raak] Whyever not? One mugger doesn't just mug one victim. They do it over and over again, as long as they don't get caught (that's probably the only practical limiting clause). There's also always the possibility they'll hit a minor jackpot, too, of someone who's carrying more than just "pocket money." I would imagine, for instance, that some of us going up to Rugby had a fair amount in cash. (As the guy collecting money for T-shirts, this is more than mere speculation!) Once they've got some money, there's no reason they couldn't invest their ill-gotten gains wisely, either, and make it grow a bit. True, I doubt most muggers are smart enough to know how to do that, but I don't think you can say it's inherently impossible to become rich through it.
[Raak] Oh, and I think you're also ignoring the way they tend to take other things the person has on them, such as credit cards, watches, jewellery, etc. The latter two probably aren't worth very much for most people (let's be honest, most people wear crap), but cards can lead to all kinds of nastily profitable shenanigans.
[Breadmaster] How about the sense of guilt? Doing something you know to be wrong makes you feel guilty. So, to put it another way, if something makes you feel guilty, it's something you feel to be immoral (this can be irrationally so, of course, insofar as any morality can be said to have a rational basis). Obviously, this isn't objective because different people feel guilt for different things.
[Darren] Ok, one can imagine how to make a lot of money at street crime, but I seriously doubt if anyone does. It's just not a real career option for anyone wanting to do more than just live hand to mouth. [Bm] What is a "should"? What are commands? The moral person would no more thrust his hand into another's pocket than into a nest of vipers. Shoulds and commands are for those who lack insight and must be told what to do. I have not (yet) read Aristotle (is this the Nicomachean Ethics?), but morality as enlightened prudence sounds right to me.