A study in 2000 suggested your average low level street dealer made $20-30k/yr [1]. That's no benefits, no OSHA, no minimum wage, no child labor laws, is frequently violent, etc. Surely things have changed, particularly with the spreading decriminalization of marijuana, but I think it's still relevant. When we're talking about restricting poor people from accepting some kinds of work, we must bear in mind that we may like their other options even less.
Heh, I wonder if a more effective way to wage the War on Drugs would be to stop prosecuting street-level dealers for drugs, but simply enforce employee status on them :-p
[1]: http://pricetheory.uchicago.edu/levitt/Papers/LevittVenkates...