I do not like inhumane punishment, but...
1) I consider rape to be one of the vilest of crimes...(I will admit this is a purely emotional reaction... I have never really known a rape victim, but I find it TERRIBLY offensive... I am against the death penalty, but when I hear about a rapist I wish that it was a death penalty crime... )
2) This jerk gave everyone in another country something to point at and say "see thats what americans are like!" He was a representative of our country and so he not only committed a horrible crime, but he betrayed us all...

I guess I hope the Japanese honor his human rights, but if he is "uncomfortable" well who does he have to blame?