There are two classes of drones. The ones which need C&C link from their pilot and the ones which fly autonomously. With the ones requiring C&C link the best bet of the authorities is to triangulate the transmitter and/or disrupt the link.

The ones which fly autonomously are more complicated. And the thread you were responding to was talking about this case. There are no commercially available drones which can fly autonomously by on-board visual navigation. The ones you linked can send a camera image back to the operator, but can't fly themselves based on that image.

what if they C&C via internet? (4g). Lantencies are low enough nowadays. Controller could be anywhere in the world.

Same issue as with a controller: jamming. Heck, they could detect the signal and just tell the carrier to shut the customer off. Would probably be unprecedented and therefore take some hours, but if the person persists, surely an option.

Oh right, the following mode! Hadn't thought of that, that surely counts as flying by camera. But it doesn't apply to the situation where you give the drone a preconfigured, uh, visual coordinates (a path, I guess that must be?) and it will try to follow it. So it still cannot wreak havoc at an airport without either you being there (follow mode), GPS being available (autopilot to coordinates), or flying manually using a remote control.