I think anyone who receives a life sentence should have the option of a humane execution in a timely fashion... Then again I think most people should have that option.
I wouldn't necessarily expect the US to do so in a humane manner though, with methods like electrocution or a three-drug lethal injection where one of the drugs is to induce muscle paralysis so you can't see the convict writhing as they die...
(Yes modern societies do know humane ways to end lives, just check the resources thread)