I can conceive of some edge cases where shooting at a policeman or a soldier using home-printed weapons does have positive expected value. But in general I agree with you - it's like wrestling a herd of rhinos.
As long as policeman and soldiers are humans, especially from the same country as you, there's the hope of appealing to their humanity to stop them from committing atrocities. Unmanned drones or robot soldiers are much scarier.
The thing with war is that the odds can change quickly. If you don't have any weapons and the enemy soldiers have machine guns, but you can sneak up behind one of them before anyone notices, now you have a machine gun.
The thing is, drones and robots work pretty much the same way. They work much more that way, actually, because if you find a vulnerability in one, it's likely present in all of them since they all came off the same assembly line. You don't have to kill all the drones, you just have to kill the ones guarding the drone control facility, or convert the drone operators to your side.
The most dangerous thing about robot armies isn't that it will make governments too powerful, it's that a terrorist could take control of them. And the only way to prevent that is to not build them.
