Each of the P are vulnerable to the same objection: What is special about robots?
P1. Killer Robots should not be produced or used in a way that allows them to fall into the hands of people who will use them unethically.
Why does this not apply to rifles?
P2. Killer Robots should not be used for any mission which you would not be prepared to assign to a human soldier if a human soldier were capable of executing it.
Again, why isn't this isomorphic to "Human equipped with weapon X" versus "unarmed human"?
P3. Killer Robots should not be used for any mission in unpredictable circumstances or where the application of background understanding may be required.
Once more: Why are "Killer Robots" different from "machine guns" in this sentence?
P4. Killer Robots should not be equipped with capacities that go beyond the immediate mission; they should be subject to built-in time limits and capable of being shut down remotely.
s/Killer Robot/military unit.
Why does this not apply to rifles? / Again, why isn't this isomorphic to "Human equipped with weapon X" versus "unarmed human"?
Killer robots pose a threat to democracy that rifles do not. Please see "Near-Term Risk: Killer Robots a Threat to Freedom and Democracy" and the TED Talk link therein "Daniel Suarez: The kill decision shouldn't belong to a robot". You might also like to check out his book "Daemon" and it's sequel.
...Once more: Why are "Killer Robots" different from "machine guns&
Peter at the Conscious Entities blog wrote an essay on the problems with using autonomous robots for combat, and attempts to articulate some general principles which allow them to be used ethically. He says:
Unpacking this a little, autonomous robots will affect the characteristics of war and make it easier for many to carry out, can be expected to malfunction in especially complex and open-ended situations in very serious ways, might be re-purposed for crime, and because for various reasons they make the ethics surrounding war even more dubious.
He even takes a stab at laying out restrictive principles which will help mitigate some of the danger in utilizing autonomous robots:
Though he is a non-expert in the field, I (also a non-expert) find his analysis capable and thorough, though I spotted some possible flaws. I mention it here at LessWrong because, while we may be decades away from superintelligent AI, work in AI risk and machine ethics is going to become especially important very soon as drones, robots, and other non-human combatants become more prevalent on battlefields all over the world.
Switching gears a bit, Massimo Pigliucci of Rationally Speaking fame lays out some common theories of truth and problems facing each one. If you've never heard of Charles Sanders Pierce and wouldn't know a verificationist account of truth if it hit you in the face, Massimo's article could be a good place to start getting some familiarity. It seems relevant because there has been some work on epistemology in these parts recently. And, as Massimo says:
This matters for anyone who wants to know how things are, but is even more urgent for one who would create a truth-seeking artificial mind.