To be fair, the…
To be fair, the per curiam opinion in Furman held only that the imposition of the death penalty in the specific cases at hand violated the Eighth Amendment for reasons unstated, because the 5 votes for overturning the death sentences were so deeply divided over the reasons. Two of those five (Brennan and Marshall) did argue that the death penalty as such violated the Eighth Amendment.
It’s too bad they didn’t win out. Not because I have any firm opinion on whether or not the death penalty is permitted by the Constitution (I suspect it isn’t, but I don’t care), but rather because it would have saved 1,000 people’s lives, and that’s more important.