Do you really think there is a risk worth mentioning that somebody escapes from the high security tract and continues to kill people? You should have more trust in your prison system. If they put somebody behind bars for life, he is in there for life.

As a matter of fact, I do think there is a risk worth mentioning. Prisons cost money, keeping a criminal fed for the rest of their life costs money. If one day prisons were forced to (say due to a hypothetical financial crisis) shut down with two options: Execute all the extreme criminals and release the minor convicts, or let them go altogether in order to avoid starving them to death, which option would you choose? Assume the same financial crisis or whatever prevents these criminals from immediately being transferred or detained before they can leak back into society, and that the prison will shut down no matter what.

You seem to be operating under the presumption that nothing extremely bad will happen simply because nothing extremely bad has happened before. Specifics aside, I think there are plenty of things that could go wrong which would result in the wide-spread release of extreme criminals into society.

Why do you even ask? You clearly don't care about those people. You are willing to kill them "for the greater good"

Ok, then let's put my morals aside, in which case, all you need to do is convince me that from a strictly pragmatic point of view, that allowing the "immorals" to live in captivity is the best option - because there is no convincing me through a moral point of view I suppose.