I'm not sure I believe incarcerated people can make free choices. And I would assume that legislators would push towards harsher and harsher sentences to incentivize prisoners to "choose" sterilization if they ever want to see daylight again.

An incarceration system, if it has any hope of working, must treat prisoners as people who can become valuable members of society in the future despite their past wrongdoing. When you decide that prisoners are a blight on society and that no rehabilitation is possible then prisoners turn into some kind of underclass that is to be disposed of, either directly or indirectly. That's real dark.