The beam is controlled by a signal beamed from the rectenna, which controls the phase of the emitters at the satellite. If this fails, the emitters go out of phase and no beam is formed.
1) That's a happy path which might or might not work during malfunction. Imagine a terrorist deliberately disabling an original control signal and then using his own control signal to steer the beam on the city.
2) Beam can be used as a weapon if you will just point it and light it up and thus deploy would be sooner or later heavily restricted or outright banned like nuclear weapons in space are banned.
