He was a terrorist who planned events that lead to American deaths. Terrorists don't get to live simply because killing them is inconvenient.
And this is a great example of how transparently inept his camp is. The "imminent attack" excuse barely lasted a day before they realized it a stunk worse than Iraq's WMD. So now it's your standard foreign guy was bad guy response.
"In a field where an overlooked bug could cost millions, you want people who will speak their minds, even if they’re sometimes obnoxious about it."