I don't see any reason to single out any primary thing to be concerned by, as there likely isn't any singular issue that can be pointed to as as the root concer

I don't see any reason to single out any primary thing to be concerned by, as there likely isn't any singular issue that can be pointed to as as the root concern regarding AI safety. Introducing millions of robots into society is something for which specific safeguards should be built. Costs related to developing such safety mechanisms seem small compared to the safety they can provide. There will be many concerns relating to AI and robotics that should be addressed by a multitude of different safeguards.