Pocketknives are not a significant threat to anyone on commercial flights.
Many men carry pocketknives as a matter of course. Imagine a terrorist faced with a plane-full of people, many of whom have a small blade in their pockets.
The Flight Attendants Union says that flight attendants can handle terrorist threats; how did that work on 9/11? I'll take my chances with aid from my fellow passengers, thankyouverymuch...