This needs a longer discussion, but you're right.
Human predators are easily identified, incurable, and time-delimited incarceration does not protect their future victims (nor the non-predators who share the prisons with them).
As soon as a human predator is identified, he should be killed (or isolated).
I agree. Often a predator can be identified at a very early age (7-12-14). And usually, they can't be rehabed. There was a discussion here once about killing such kids. Don't think I could live with that. But locked away forever doesn't bother me a bit.