Well said Robert. Don't forget that there have always been high-rate loans available to high-risk borrowers; pawnbrokers and loansharks.
Poor preyed upon? The "poor" are the largest element of lottery ticket purchases, thus voluntarily paying additional taxes. Funding your schools, et cetra. Speaking of taxes, without payroll witholding (implemented in 1943 as a temporary measure), the poor wouldn't have any savings (getting most or all back in the form of tax refund). Stated another way, a princely portion lack self-discipline, thus fostering one of many stereotypes. Payday loan locations serve a purpose. They replace loan sharks under a street lamp. Hence less broken bones.
Saying that people do stupid things in no ways implies they should be prevented from doing so by the government, especially since it's elected by those very same people.
When it's no longer profitable. I think the best we can do is to make sure that any financial mess is compartmentalized. Basically, I don't care what you do to screw yourself, as long as your problems don't spill over and cause me grief.
It isn't just the poor. For the middle classes it is designer clothing, "status" goods, real estate aspirations, etc. Wealth is transferred by exploiting the vulnerable and the stupid at every level of society. Trading is another aspect of this. Who loses? Usually middle class professionals with decent income and some savings to "dabble" with.