Interesting topic..... full of emotions, of course. The death penalty would certainly make a martyr of such a terrorist. And the arguments against it generally because of the risk of wrongful conviction I agree with. I'm also reminded of the saying from somewhere or other that goes "There is no point getting your own back on someone if it means stooping to their level to do it".
For myself, no matter how cushy life in prison may be in western countries, the deprivation of liberty should never be underestimated as a punishment. On this site we are all travellers. If we were put away for 6 months or a year, MAYBE we could handle it... but I know damn well what would happen to me if I got sent down for life. As for Moussaoui and other extremists, rather than make them martyrs, by all means protect the public by keeping them in jail and for the actual punishment, how about showering them with western kindness? Given their views of us infidels, it might just send them all more batty than they already are.