The original question has certainly been answered well here, but I'm going to add my 0.02USD anyway...

1) If the plane makes and unscheduled landing, I plan on walking away from it. I also plan on surviving the environment in which said landing takes place.

2) If someone tries to hijack the plane, I plan on doing something about it. If more people had this attitude the events of 20010911 would likely have been less severe.

3) I'm a citizen of the United States of America. It's my right to bear weapons. Period.

4) Luggage gets lost, sometimes.

I much preferred the days prior to 20010911. The days when I could just give my knife to the stews, who put it in the pilot's lockbox for safekeeping. Of course, my knife in my pocket would have been even better, but at least it was preferable to the lunacy that passes for "security measures" nowadays.

When I went on my honeymoon to Italy last year, I got hassled by the "security" drones at EWR about my Brunton Helios lighter, after having passed through the security check with it three times while waiting for my flight, even though I was clearly going outside for a smoke. God, they even asked me if my pen was actually a pen! Not that they pulled the cap off and checked, they just took my word for it. You call that security?! Then it was my carabiner, which many travel resources recommend you use to clip your bags together to prevent airport theft. It was claimed that I could use it as "brass knuckles". They eventually let me keep everything, but only did a cursory check of my carry-on, which was loaded with all sorts of odd things, like two Snow Peak Titanium Sporks, a shortwave radio, a couple of more cigarette lighters, a Storm whistle, a Black Diamond ATB rappelling device, lots of cord, some 9mm rope, etc, etc.

What really irks me is that although walking canes are specifically allowed by reg.'s, I'm sure that if I walked up to the gate with Cold Steel City Stick, with it's stainless steel head (which won't pass the metal detectors) and it's fiberglass shaft, being a healthy 34 year old who doesn't walk with a limp or generally wear a top hat and tails, I'd likely get thrown out of the airport, or worse.

Want to stop terrorism? Arm the populace and make sure they know the responsible use of their weapons. Our current society is more disposed to turning out ranks of sheep who are so afraid of violence and/or their own inability to control their own behavior that they would rather willing give their lives over to people of questionable motives--like policemen, politicians, and terrorists.

Okay, rant over...

If you think carrying a PSK on a plane is unnecessary, I hope you never find a need to use the sorts of things one generally contains.

One of the best mottos I've ever heard is the motto of the Boy Scouts of America--Be Prepared. That just about covers everything in life, doesn't it?