The prison system in the U.S. sucks for a number of reasons. Politically driven war on drugs (MJ), little opportunity for ex-cons on the outside, mentality gained on the inside, the public defender lottery, and the list goes on. All lead to over population and an enormous cost. IMO, the solution has got to start with a reason for cons to get out and go straight in the first place.
Short story: I spent 3 years jumping through legal hoops to "be allowed" to hire an ex-con. Once I got it legal, my CEO and HR Vp called me in and basically told me if there was a problem, it was my ass. In the guys 2nd quarter employed with us he was named employee of the quarter out of 2500 employees. When we were getting ready to give him the plaque, the CEO asked who he was. I told him. While not always as successful, that opened the door for me to hire more. To my knowledge the guy is still there 15 years later. But now, the liability alone prohibits industries such as mine from hiring ex-cons. IMO, that's a big part of the problem.