In general, when you're presenting your opponent's ideas as this level of two-dimensional magical thinking, you probably haven't engaged with the ideas enough to have this strong of an opinion about it. The prison abolition movement has been around for a long time, and has indeed grappled with the idea of "but what if someone murders someone?", which is indeed the absolute first question someone arrives at when considering prison abolition.
Even if you give murderers the Anders Breivek treatment with a cushy apartment style prison cell complete with gaming consoles and arts and crafts sessions, that's still a prison cell. You can dress it up to make it pretty, but he's still locked up, taken out of society, which is what both he and society deserves. If that is what is meant by the abolition of prisons, then it should be called prison reform instead. Prison reform I can get behind, but that's not what is actually being proposed. That's the motte the prison abolition radicals fall back on when challenged, not what they're actually calling for.
They're talking about criminals being housed in something other than a tiny cage with other criminals 23/7, who are all treated like they are irredeemable criminals who should never be allowed to re-enter society, even though most of them don't have life sentences. Turns out if you do that, the micro-society that results among prisoners is a warped society where criminality is rampant and normal. The strategies you learn to live in the prison society will cause you to become more of a criminal once you are released into the larger society, not less of one. In other words, prisons as they are currently run in the US are effectively a crime training program.
In what world is that logical? In what world would we not ask ourselves, "Is this really working? Should we at least try something else?"