We have to go two steps back before addressing the issue of the scissors. First of all, aviation is a global product, and it does not matter what a certain country, airline, or airport perceives as a risk. In order to harmonize, there has to be a global understanding about what can and cannot be brought on board.
If I have a bad intention, I can hijack an airplane with my glasses. I can use them to stab anyone, and then I can open the cockpit door and hijack the airplane. I don't need scissors for that, and there are probably more skilled people who don't need even the glasses. They can do it with their hands.
The question is the international understanding of the risk and the steps needed to mitigate it. We need to determine the list of allowed or prohibited items. If I had a pair of scissors, I wouldn't hijack an airplane, but I also don't hijack airplanes with my glasses. If I had a gun, I would not hijack an airplane either.
It is the intention and the information that matter, not so much the list of items. The list of items has to be agreed on globally and has to be implemented globally. Otherwise, it cannot produce a global product.