I'm fine with the assumption that most travelers are not going to hijack - or blow up - a plane.

If they want to be stupid and bring a firearm in their carry-on luggage, then they're no longer trusted, and can be subject to the stricter (currently standard) lines for a 10 year period. They asked for it by breaking the rules.

Unfortunately, you just know some over zealous TSA person will throw the book at granny for bringing those mass murder capable nail clippers with her, and we're all back here again.