Autonomous killer drones are already a possibility without a hypothetical AGI.
It really changes nothing. Proxy wars fought via drones is modernity. The thing that does change it the ability to spread propaganda online like never before.
Look at stuff like Qanon. You don't need an argument that's very sophisticated, just a lot of it and the ability to promote it at scale via hordes of undetectable bots. Current generation free models are good enough to do all that.
People are either going to learn to become skeptical or they're going to be manipulated at massive scale. We are already there and arguably have been for a while.