I've never been personally a fan of the death penalty only because the risk of offing innocent people. There's just no going back from that, and frankly, you have to look no further than the Trayvon Martin case to understand how fine is the line sometimes on some of these convictions... The wrong jury can send you straight to .
On the cruelty aspect, it's just another avenue to pursue delays. While my personal feeling is that perhaps it's more cruel for them to rot in jail, the reality is that the amendment provides a route to challenge deathrow that's not there in jail for life, and it's unlikely to go away due to the fact that changing the US Cons ution is a difficult process. This is reflected in the SCOTUS having to tackle the 8th amendment many times when it comes to the death penalty.
But that is also why States that have the death penalty try to pursue a known, proven, minimally cruel method: it cuts down on arguments on appeal. With all these botched executions, now you have new arguments on appeal, and you can bet every inmate on deathrow is going to be applying for that . Now you have more delay, etc.