I don't think the problem is with AIs acurrately identifying friends and enemies. You can't solve that 100% anyway, but if it can aid humans and prevent mistakes, all the better. The problem is when you start to build absolutely relentless border drones that can one-shot the enemy, without any possibility for mercy or negotiation.

With weapons, the desired outcome is not to kill, not in most circumstances anyway. In circumstances where it is, it is almost always the desire of an individual wielding a weapon. Normally, the desired outcome is deterrence or defense, and when used proactively, to lessen the enemy's ability to continue to wage the conflict. With deterrence, the threat of death is the deterrent, with defense, killing is the machanism by which the threat is neutralized, and with proactive aggression the goal may or may not include killing, and is more likely to include killing if the enemy's ability to wage conflict is dependent on manpower. In all three scenarios, the desired outcome of developing autonomous military capability is to save lives.

One maybe stupid example is when there were lots of Syrian refugees on the way through Europe in 2015. We learned the hard way that, if people are pushing against your borders, the only way to keep them out is to eventually use force. We were not willing to do so, so we had to accept that and grant people asylum (which I think was the right decision).

Imagine (a bit scifi but for the sake of argument) "border patrol 2000", which will give a warning, then give a more stern warning, then raise a wall, then try rubber bullets, then try to keep you from climbing the wall with a grappling arm, and finally using live rounds. If you are really determined it will eventually have to shoot. Human solderies did shoot in the past but they did also sometimes not shoot, and it always had a political aftermath. But with automatic systems, it is too easy to psychologically detach, and to say it's e.g. the refugees own fault.

Also, having people in the loop reminds at least someone that this is 'real' and that we need to carry on thinking about it. If you can obliterate enemies' bodies and the only duty on people is to restock the ammo I think that reduces the moral burden of conflict in an unacceptable way.