is it because people think it is inevitable and there is nothing they can do to stop it?
or is it because people think it is fantasy and could never happen?
Will this capability exist? Yes, probably.
Am I concerned that this capability will be deployed against me? No, not really. Theoretically it could, but then again, so could a dude with a gun. I live in a democratic first-world country, the capabilities of my own government are likely to exceed the capabilities of those who want to kill me. And theoretically maybe my government might want to kill me... but it could already do that anyway, using a dude with a gun.
For now. Things change.
Phalanx doesn't work tho' :-) In 1991 Iraqi forces launched a Silkworm missile against USS Missouri. The ship launched decoys... and its Phalanx guns promptly targeted those decoys. Fortunately there was a Royal Navy ship, HMS Gloucester, in the vicinity which dealt with the problem with a good British weapon, the Sea Dart missile. This was the first real "drone on drone" combat, if you will.
It also fits the progress we've been making - we removed civilians from the battlefield or at least we made it a war crime, and now we need to remove soldiers from it too (especially considering that they will become inferior - slower reaction, no 360 vision, slower speed, can't fly, can't really network and exchange full tactical info, etc. - to drones anyway). Let drones fight each other.
For non-military setting it was already addressed in South Park for example - autonomous police drones will control the airspace. I think in the future any UFO will be just taken down like a car without license plates.
In the Middle East, the US likes to blow up buildings that they think might have terrorists in them with a drone-launched missile, then have the drone circle back and hit the rubble with another missile a few minutes later to kill any neighbors or EMTs coming to help the victims.
> Let drones fight each other.
Are you imagining a sci-fi future where nations politely agree to decide their disagreements with bloodless robot duels? Wars are won by destroying the enemy's will to fight, not by gentlemen's agreements.
You seem to think that war can be made safe and civilized somehow. It reminds me of the 1897 New York Times writer who thought that machine guns would lead to peace on earth because leaders would hesitate to send their soldiers against such deadly weapons.
Where is no "politely agree" nor "gentlemen's agreements" in international relationships, only sheer power. MAD is an example of power forcing to not fight a war at all. Falkland war was fought without bombing Buenos Aires or any other action outside of immediate war zone. Ukraine/Russia war in Donbass was limited to that area because of possible repercussions to either side for letting it spill out (and for the same reason both sides in general, with some exceptions, didn't indiscriminantly target civilians). US and other developed countries limit sending its soldiers in harms ways and hitting enemy civilians because of internal and external political repercussions. So it is always a power calculation, and as a result in this more and more interconnected and densely populated world we have 2 tendencies - restricting conflicts to specific localities and minimizing human involvement. Those 2 tendencies ultimately lead to drone wars confined to specific areas (preferably in space or in cyberspace - notice how much of adversarial activity happens more and more in cyberspace, yet nobody is going for real life action over it). Attempt to bomb each other's cities will be (and pretty much is already today) unthinkable like in case of Falkland war. Of course, when there is no containing power in sight, we immediately have what Saudis do in Yemen right now - it isn't even a war, it is just pure genocide.