fragile white liberals can point to it and go ‘See? Prison labor isn’t that bad!’

I just don’t see any liberal type (I’m assuming you mean progressives – just basically the opposite of trumpets) saying American prison labour is good. But they may say that if decent and meaningful labour at union-like wages has been shown to be beneficial for decreasing recidivism, then let’s trust the science and get some oversight and assessment going to confirm or refute it.