The stance held by Google engineers seems to be more subtle than that, although it is fairly clear: a weapon produced by an American company may go either to kill a civilian in a pointless war in a country nobody has ever heard of (high-probability), or to kill a Chinese soldier in a future war for the survival of our country (low-probability). The US government could address this by improving the mix ratio between pointless wars that benefit nobody and wars for the survival of our country, so that a weapon would be more likely to end up used for the latter than the former.

Sure, but it is defensible that a greater balance of power might be a net good for the world. (Also the devil is in defining net good). And it is also quite defensible to restrict hard power to ethical channels. There's a reason we don't use chemical weapons even though they would definitely give us an edge: The moral harm outweighs the tactical benefit. (Until it doesn't, as we saw in Syria.)

Militaries may be a necessary evil, but in no way a force for good.