There's an infinite number of ways to asymmetrically attack a system. A single person in Australia caused millions of dollars of damage by just sticking needles

There's an infinite number of ways to asymmetrically attack a system. A single person in Australia caused millions of dollars of damage by just sticking needles into strawberries in supermarkets. People have rented and driven light vehicles into crowds. People have deliberately poisoned food at restaurants. The attack surface is limited only by the imagination, while defending against each scenario carries immense financial and personal freedom cost. The whole point of asymmetric attacks is that they use the size of the target against it. It's impossible to stop these kinds of attacks without completely taking away personal freedoms and instituting some kind of pre-crime surveillance state. And a pre-crime surveillance state is exactly what most governments seem to want to build today. The historical scales are rapidly tipping towards tyranny in the name of illusionary safety. As Franklin aptly put it, "They who can give up essential Liberty to obtain a little temporary Safety, deserve neither Liberty nor Safety". As far as drones go, it's comparatively simple to build what's effectively a supersonic missile for about 10K usd worth of easily obtainable hobbyist parts. It's been possible for the better part of the decade. The fact that no one has done it suggests that maybe there aren't that many bad actors out there after all.