If there's one thing that's typified a few recent spree shooters it's that they've let themselves be taken alive. Using a drone takes that possibility completely out of the equation. If they were only deployed on people hell-bound on mass destruction, that's one thing but we all know it won't stop there. They'll be deployed against gang activities in major centres. And it's not them assisting police ops which is as much a problem as them (eventually) making operational decisions themselves.
Mind you, there were protests along similar lines when police started using helicopters and IR vision in the 80's, etc. so what the hell.