Same issue: a world where the technology to build an incredibly cheap drone that size which can hunt humans with facial recognition based on specific parameters exists...is also a world in which an anti-drone can use the exact same technology and just ram into unidentified drone vehicles to disable them. If the swarms are cheap enough for terrorists, then the counter-swarms are monumentally cheaper.
EDIT: It's worth noting you could argue other scenarios - like only governments building these, but that's what I mean by the message being confused - it's not clear what the threat is supposed to be.