There was many a time I wanted to. Many a time me and a friend "planned out" some robbery, only to figure out another way to get high and quickly forget all about our plans.
But I did meet a guy in detox, who made his "drug career" so to speak out of robbing dealers. Heard quite a few stories. He refused to pay for drugs. Cant say I think its a terrible idea, or that its against karma somehow: I mean a dope dealer selling someone poison obviously doesnt give a fuck about you, why should you give a fuck about them?
THATS the karma to me, for the dealer at least, though I guess youre right, the other guy'll prob get it in the end too.