It doesn't sound viable in the least. This literally sounds like something somebody over on Spacebattles came up with.
"Dude, we should have robots guarding our schools. "
"Unarmed? What good is that?"
"But, it's a *expletive deleted*ing ROBOT. "
You arm these things, and I'll start shooting them pro-actively. Dead serious. Even if they only have tazers or pepper spray. Remote compliance devices? Area-of-effect mace or pepper spray? No effing way.
If *I* armed the damned thing, it'd only be because it was watching my lawn. I'd also be sure to upload the Clint Eastwood / Walt Kowalsky voicepack to it.
"GET OFF MY LAWN. "
Seriously (and I really can't take this idea very seriously, because REALLY? ) this is the epitome of a pipe dream.