A lot of people don't have a choice otherwise, except homelessness and poverty. Not exactly a 'free' system. Runaway free market Capitalism creates this problem as it sends money to the very top leaving the rest to fight for a small portion of the pie. Working is not voluntary in USA unless you already have plenty of money, or are supported by someone with money.
>to some extent it is impossible to prevent them because of scarcity
There's no such thing as scarcity of pretty much anything in USA. We have 18.9 million vacant homes, with 3.5 million homeless [1]. We throw away 150,000 tons of food every single day [2]. There's no scarcity there, it's just capitalism at work.
I'm putting the blame on the correct ideology. None of this would happen under a sane system with checks and balances. What you're seeing right now is _raw capitalism_ at work.
[1] https://www.huffingtonpost.com/richard-skip-bronson/post_733...
[2] https://www.theguardian.com/environment/2018/apr/18/american...