People stopped flying after 9/11 and airlines lost money until the TSA was created and made people feel safe to fly again
I'm no chemist, but I can't imagine it's hard to test if something is an explosive or just body cream. To pack a punch, I have to imagine explosives need very specific compounds in them.
2) might want to look up how often firearms make it onboard in carry on bagage accidentally. This isn't the typical snarky use of that phrase- it's just so insanely common people don't want to beleive it.
I think it's perfectly reasonable to forbid >100ml of acetone in flights, and allow people to bring in, say, a bottle of water or a can of orange juice. We can certainly test if something is acetone or orange juice.