Personally, I'm not necessarily against the penalty but rather the system and how corrupt / wasteful it is. I think we need to separate the system that deals with the person from the act of removing somebody from our society. A lot of innocent people get executed, and scores more get life in prison. The appeal process is lengthy and costly, not to mention traumatizing for the family. Those who need rehabilitation need rehabilitation, as our mental health industry is also quite broken. I think that's where money should go, not to giving offenders room and board or to locking away the innocent.
That being said...
If we have you on video setting a bomb that kills children, if you are unrepentant in the face of crying family members of the victims, and if you after the act still think that it was an appropriate statement or action to carry out in the name of what you believe...we should line you up out back after court and nail the cheapest round of ammunition we can through your skull. Don't waste another cent or hour. There are over 7 billion people on this planet, and we don't have the time or resources to fuss around with the likes of Tsarnaev.