Therapy is only worth the cost if the murderer gets released from prison. Even then, not a lot of people would be willing to hire him. However, if the criminal's family is willing to pay for it instead of the government, I am OKAY with it.
Also, as Qwepir said, the murderer probably killed a "productive member" of society who was probably more productive than the criminal will ever be.
The only reason Norway has less criminals is because they give the citizens a forget ton of welfare including the rehabilitation, and it's actually causing the nation to go broke.
cheapest answer to sickness is to not treat people and let them die
Except most good Americans pay for their medical insurance and doctors instead of letting the government pay for it.