> The private prisons are contractually guaranteed a minimum number of inmates for example, and you can even buy stocks in them. So then if you are a shareholder, I guess more crime is than in your financial interest so the prisons you own a small piece keeps making money.

I don't think so. Private prisons hold less than 10% of total inmates, so there's no way they'll be short even if suddenly the US started to jail half the people it does now.