Well since we practice Aikido as a Martial Art I sure think there are techniques that are just as "deadly" as a heel hook and our Ukes are taught to keep attacking till they are pinned or subdued...
So sorry folks but I guess I basically disagree with everyone except David and the Shodothugs.
The "deadliness" of Aikido is congruent with it's application. The way Aikido is applied in most cases is not Martial in practice or approach but that is the fault of the Instruction and when folks complain about Aikido not "working" I can't argue with them if all they see are pony tailed dancing Aiki Bunnies hopping hither and yon on fields of green rubber tatami.
Shoji Nishio Shihan saw this as a paradox we could work with...Aikido must be effective against other Martial Arts otherwise it is not a Martial Art and... It also must "express" Aikido.... So practice is about beating your swords into plowshares so to speak.