Gambling and loan sharking are the twin pillars of organized crime.

The customer base is huge whether it be numbers,sports,illegal casinos or in some cases,guys that need money to expand/start a business or to pay off personal debts and can't get a stick of gum from the banks.
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The profits are steady and very lucrative,and in most cases,the criminal penalties are not that harsh.

A guy can earn serious money while staying away from the more "criminal" type stuff. Build up a nice business,kick up to whoever you have to kick up to,and in a few years - Bada Bing,Bada Bang,Buttafucco !

You got a nice stash and instead of eating mystery meat in the joint,you get to bounce the Grandkids on your knee at your Condo in Miami.