Dylann Roof sentenced to death

[abaris]

If his mental illness causes him to kill people, then obviously he shouldn't be allowed around other people. Including more sane people in the prison system.

That's why folks like Brejvik are isolated from the general (prison) population. You don't have to put them down to achieve that task. In fact, people like that should be studied to the fullest in order to prevent others from going down the same road. It's a known fact that serial killers can't be rehabilitated. But they still can offer valuable insights. In Europe they're confined for an indefinite period of time at a secure mental facility after their sentence - which is usually a stretch of 25.