In response to the OP, I do not believe they should be executed. Trying to solve the problem killing by perpetuating more killing is asinine.
"An error does not become truth by reason of multiplied propagation, nor does truth become error because nobody sees it." - Gandhi
It depends. I'm not too comfortable with the idea of using a label to justify executions, since the definition of the label can be manipulated by the government, but on the other hand, someone who is a real terrorist should be executed; I'm not sure where that leaves us...
Then, after a time, cool and calm minds prevail, usually.
Imagine the world's population if "Death in either case" were to prevail.
With these terrorists, we must do to them the very thing they fear, which is not necessarily death.
I'm against execution in general because I am against giving the government the jurisdiction to decide if a person should die or not.
Aside from that, executing terrorists would just be a sign of the political times. It still comes down to whether or not the people they murdered warrants death, and it all depends on what state they are in as to whether or not a death penalty sentence gets delivered. It's all arbitrary and inconsistent.
The only way you'd get universal execution for terrorists is in the Federal government makes binding legislation that overrides the sovereignty of the states; or, if the states, miraculously, all decide that they'll execute them. Which do you think is more likely to happen?
So I'd say no.