While I don't know everything about either the US or NL prison systems, I have lived in both places and do know both a guard at a non-maximum security correctional facility in California, and several psychologists who work at TBS 'clinics' in NL. For non-Dutch, these TBS clinics are where many dangerous criminals can be held for longer terms than are normally associated with the punishment for a given crime, based on the fact that these people are mentally unstable and likely to commit a crime again.
The differences in the criminal systems are huge. I agree that a great way to judge a society is by how it treats it's inmates, and that this could certainly be improved in Holland... but comparing the prison systems in the US to NL is just ridiculous.
Sentences are incredibly short in NL compared to US. There is a focus on re-entry into society, not so in the US. Life-long imprisonment is extremely rare in NL, with most cases being people in TBS clinics under supervision and care of psychologists, psychiatrists, and social workers. There is no death penalty. The incarceration rate is 8x higher in the US.
Violent criminals in the US are sent here: http://news.nationalpost.com/2012/07/11/group-therapy-cage-m...
Violent criminals in NL are sent here: https://www.flickr.com/photos/omroepbrabant/sets/72157624396...