You have to remember that a nasty terrorist can cause all sorts of nasty harm to all sorts of normal everyday things. A few seconds thought will prove that. In general there is nothing you can do except prevent these things happening in the first place. That doesn't mean you can't disagree and live your life a different way. It just means don't stir up the hornets nest. Unfortunately many events have stirred the nest, and there will be some pretty nasty things happen in the future. What those are is anyones guess, the fact remains we cannot prevent them all and just have to get on with our lives. In many cases the prevention is worse than the act and in that case they have won. At the end of the day ALL security systems depend on trust. Adding extra "security" to prevent your imagined scenario will only curtail innocent people's lives - something millions of people died to protect. Terrorists don't abide by laws, so legislation often only harms the innocent. I can't see how we could introduce anything that would solve your scenario without curtailing otherwise peaceful activities to all our detriment.