So potentially non-lethal means of self defence are bad, but a weapon that can slaughter a classroom are A-okay. As a Canadian, American logic is kinda terrifying.
It will likely be overturned on appeal, as they might have well interpreted arms as the things attached to your shoulders.
These "non-lethal" weapons are more likely to get you hurt than either disengaging entirely or engaging with a deadly weapon--to wit, one of the reasons they have officers and MPs go through CS gas/mace is to show them that they remain functional and as such they should never assume that somebody they've used a non-lethal weapon on is incapacitated.
Which is, by the way, not what direct observation of evidence suggest. After all, baseball bats have been and continue to be much more easily available than tasers, and still you do not see hordes of drooling-idiot teenagers hitting people for fun on the streets.
What you see is a small minority of very troubled kids attacking people for more or less rational (or at least, purposeful) reasons with whatever weapons happen to be available to them, more or less regardless of lethality of said weapon. And you are not going to solve that problem by making sub-lethal weapons unavailable to a completely different demography. What you do is to identify those kids and rehabilitate them before they become hardened criminals.