The threat of terrorism isn't by the amount of people it kills. It's the immense psychological, economical, and political impact it has. People don't like other people killing them, or forcing crazy-ass ideas on 'em. That's terrorism. So, it's of the utmost importance that terrorists are neutralised.
There's not much you can do against people falling down stairs. But there's a whole lot more you can do against criminals, of any kind.
