It's self-evident that most of the actions of the criminal justice system are cruel. I think anyone would agree. However, that phrase in our constitution explicitly leaves the door open for our criminal justice system to perform cruel behaviors, as long as they are in line with the standards of the day (or, if you're an originalist, of the standards of 1791).
So, my response would be that you've tabled the only portion of the debate that is relevant. I'll freely concede that the criminal justice system is cruel, but I wouldn't then argue that the system falls afoul of the 8th amendment.
States convention, anyone?
I think there's a ton of opportunity to totally re-work the criminal justice system within the confines of the current amendments. I think that kind of change would be a lot more politically feasible in the near-term (as in, you could make such changes with 45-55% of the population's acceptance, rather than 65-80%).
The 8th amendment says "you can't be worse than X", but it doesn't put any constraints on how "good" we can make the system. I think the political reality is that we need to improve the system significantly before we can constitutionally constraint ourselves to that new bar.
Imprisoning people who have committed crimes is not cruel. It's literally the job of every justice system to do that.
If there was some sort of abuse then sure, but there hasn't been to my knowledge.
This makes it usual or common, but it doesn't make it not cruel.
> Imprisoning people who have committed crimes is not cruel.
Imprisoning someone is absolutely cruel. It may be common and accepted (and it certainly is in our current criminal justice system). It may even be just and proper, but it is still cruel.
That's not what is being called into question. It's imprisoning someone for the express purpose of coercing testimony that smells here.