How is it forgeted up? What the Tsarnaev brothers did was forgeted up, not killing them for their actions. It's deserved, heck if I were the judge - I'd allow much more to be done. The death sentence in this instance is too good for the guy.
Because you're condoning torturing another human being for amusement.
A deplorable and terrible human being, yes, but it's still a stuffty thing to do. Just because you do something bad to a bad person does not make that act right.