Frankly, I think we need to think about "cruel and unusual" for a second.
What is the one thing that every human being does? Die. So, it's not unusual to die. However, very few people get locked into 10x8 cages for 23 hours/day, for the rest of their lives. That's "unusual".
And, which is crueler? To die peacefully in your sleep (when given proper drugs), or to live day-after-day, in a cage, terrorized by fellow inmates and jailors?
I'm not meaning this as a realistic argument for/against anything. But, it is odd that we tout up "cruel and unusual" as a reason to ban death penalties, when life incarceration is, by any rational standard, far crueler and more unusual.