DISCLAIMER:I have an unhealthy, Hugo Strange-esque obsession with Batman. If you're uncomfortable with the idea of someone hyper-analyzing the psychology of minor, unnamed comic book characters, you might wanna give this one a pass. Fair warning and all that.
I can't imagine working class crime is much of a growth industry in Gotham. As if the presence of Batman wasn't enough, there's rival gangs, frequent cataclysms and, of course, murderous, psychopathic supervillains as one's primary source of employment. Despite all this, however, the market seems to be flooded with thousands upon thousands of repeat offenders, cheap thuggery with little or no hope of progressing up the chain of command or even making a decent living who continually return to the same rackets and the same syndicates time and time again.
The Batman offers broken bones, compound fractures and inevitable detainment, once again, to Blackgate Penitentiary. Barring, say, The Riddler or some of the less brutal mobs, practically every crime boss, from the Roman to the Penguin to the Joker, all boast disgustingly high turn-over rates for their gorillas and bodyguards. Assuming the normal forces of law, order and due process don't put an end to your career, there's still the infinitely wealthy and seemingly omniscient masked vigilante with mastery of every known martial art and a bottomless bag of hyper-advanced weapons to contend with, not to mention the escaped homicidal psychopath who's equally, if not more likely, to kill you as write your checks.
Still. I bet Gotham City goons don't eat Ramen for every meal.
(Edit: Weird formatting issues. Apologies.)