That's all well and good if you are dealing with a terrorist. But if it's some idiot in his backyard spotting planes (check back a dozen posts), a grenade or two isn't going to make good press for your airline/police department. 90 seconds on the evening news, with video of the amateur being led off in handcuffs will probably suffice in such circumstances.
Problem is, at the time you most likely will not know if it's a terrorist or an @hole.