Because it’s utterly dehumanising for the operator. Plenty written about the negative mental health effects on drone operators.
And how does a remote operator assess the scene so as to decide deadly force is the only option?
I must admit I lean this way WRT gun control in America. The solution is straighforward. If they choose not to adopt it, that's up to them. It's like wearing a coat in the rain. It's the obvious solution, but if you elect to walk round in your shirt then don't be wailing and gnashing your teeth when you get wet.
Because a bomb disposal robot deals with bombs and not living people. If a robot blows up my car because it wrongly thinks it's a bomb, i need a new car. If Robocop shoots my mother as she is engaging in hand to hand combat over the last lamb chops at the butchery counter, it's a bit harder finding another mother.
I don't think any of us have direct competence on this subject, but one could suppose that an officer who not in immediate danger of being killed or maimed in a split-second context might make cooler and reasonable decisions.
