This came up at the AI Ethics panel at AAAI, and the "outlaws" argument actually seems like a fairly weak practical counterargument in the reference class that the ban proponents think is relevant.

Disagree. It only seems that way because you are looking at too small a time scale. Every time a sufficiently powerful military breakthrough arrives there are attempts to ban it, or declare using it "dishonorable", or whatever the equivalent is. (Look up the papal bulls against crossbows and gunpowder sometime). This lasts a generation at most, generally until the next major war.