There's very little probability there will be 2 bombs on one plane , right? And I will definitely not detonate mine, therefore making the whole flight safer...
Joke aside. I think if someone is able to take over plane with scissors or box cuttters or whatever else is banned, they will be able to do it without it as well. It just takes a bit more effort. So why bother with such draconian rules? Scan people for IEDs and firearms and that's it. In addition strenghten in-flight security. For example someone trained for close combat in such scenrios will be travelling as part of crew or undercover on every other flight.