Drones can bring down a plane, but should be custom-made (it has to be fast and explode on impact and ideally used on the landing stage of the plane because intercepting a plane with a drone midair is impossible unless you make a jet powered VTOL or rigid wing) and terrorist in general don't go too techie, they just pick a van and roll over people, pick a gun and shoot or just strap some C4 to their bodies at then go boom.
It's just a matter of time, one day a drone will kill someone in an accident, and a drone with an explosive attached will be used on a terrorist act... and what? The problem is not the tool, is the person behind it. 1.3 million people die each year to car accidents worldwide, cars and vans are a common tool for terrorist attacks and yet everybody use them on a daily basis and nobody needs to emmit RID at 2Km around their car.
On the later years we've reached the point that every flight incident has been caused by drone, it's always a drone till proven contrary. They just want to ground our hobby to clear the <120m airspace for the big companies to exploit freely. All the rules we have now, the RID thing, the bad publicity, the karens (now armed with karen apps), the only purpose they seek is to kill the RC hobby (well, at least the flying part of it XD).
I think we should stop calling our flying tripods "drones" and use reserve the word "drone" for military equipment like the predator, that way we would draw a clear, big bold line between what is a flying camera or a model and what is a flying weapon.