A little of both. If you have bad credit and need cash fast, that's probably the only way. The bad part is that the interest rates are much higher, but that's also to minimize the risk of loaning money to people who aren't "credit-worthy."
It's something else to exploit the low income, stupid, and/or addicts. The world was probably a better place without them. No need to start listing all of the times they help someone out. Sure they do occasionally. I have a family member who was cashing his paycheck there twice a month because he got paid on Friday night when he got off work. After one conversation he now has a checking account at a bank which is open on Saturdays. No problem and much smarter.
Those fast cash and check cashing places are one of several key signs of a neighborhood devaluing itself. College towns not included. That is where my family member live. Many students who also work do what he was doing.