There's no reason for scare quotes given the specific carveout for slavery which exists in the Constitution. If you have an issue with that verbiage, take it up with the 38th United States Congress and Abraham Lincoln.
> do murderers get to walk free?
You're arguing against an extreme position that nobody actually holds. Most reasonable people would probably point to criminal justice as implemented in many European countries as exemplifying a more humane model which produces better long term results.
The carveout for the enslavement of incarcerated people also created a perverse incentive which played out predictably in the wake of Reconstruction's failure. If you're interested in the long and painful history of this fact here's a useful resource: