Ah, that's a convincing point, but I've always felt my answer actually opens up the door for important discussions like :

-Historical // between slavery and prisons -Partial rebuttal of the question itself, or rather, its framing of the issue, my underlining it's completely legitimate to advocate for the abolition of something without having a plug'n'play replacement for it

-Usually, people will follow up by highlighting cases of pedophiles and rapists, which could further be used to frame the discussion with them : who are we talking about?

-If I'm in a bad mood, I'll also ask people : "My brother in Christ, weren't there folks around who thought slavery was indeed created to solve an actual problem?"

But yeah, that's only the first part of my answer, then we'll move to the more grounded post-carceral society discussion.