I don't think that's the rebuttal you think it is.

GP's argument is usually used in the sense of "if I hadn't done it, someone else would, so I might as well do it and the end result will be the same, except then I'll reap the rewards".

It's a crap justification for doing something unethical. But in many cases, even the unethical ones, it's also true, and I think in this case it is too. If the US had magically shut down every AI lab on day one, and banned all AI research, that wouldn't have stopped this train. Probably would have slowed it down, but not enough to really matter.