Earlier quoted context omitted.
There are plenty of countermeasures, but they're all active countermeasures - ex. a couple guys with shotguns, trained falcons, or your own anti-drone drones.
Yes, but kinetic countermeasures scale really badly. The definition of "drone" is also quite flexible here, a couple guys with shotguns, falcons, or your own anti-drones work fine against a few slow drones, badly against a few dozen slow flying drones, not at all against a few hundred slow flying drones, are essentially useless against one jet-powered drone (microjet engines are very cheap!) don't have a hope against…
Just imagine what destruction a terrorist can create if he can launch a 100 drones, from miles away, to attack a filled stadium.