And do you think that somebody who packs his drone with C4 and aims it at passenger aircraft is going to care if he is violating a flightpath? Forbidden is not the same as impossible.
Right but 'it is illegal to put a drone in this airspace' gives us permission to shoot down anything in a flight path before impact, including the ones with C4.
What weapons does one use to shoot down a toy drone? You can't miss because on the other side, there are people, and if it hits, it shouldn't lead to dangerous parts all over the runway.
And maybe the energy necessary to actually vaporise entirely would not be the kind of thing one would be wanting to punch up into the atmosphere willy nilly.