I don't think there is any evidence at all to suggest that executing terrorists has ever had any effect other than to promote terrorism. It just doesn't work. If capital punishment is about stopping people murdering other people, terrorists are the worst candidates to pick for it.

Timothy McVeigh - as I read it, he's adopted the officially sanctioned military attitude towards civilian deaths, down to the term "collateral damage", and has imported it into his own personal campaign against the US government.

Horrible, but not all that different from the mindset of generals, politicians, and for that matter of many (most?)ordinary citizens who support the actions of their governments without question, even when that involves large numbers of totally innocent people being killed.