JWs teach that lethal force can be used to protect themselves and their families. That they seek to avoid doing so unless absolutely necessary may be a fine distinction, but one many could understand.
I think most pacifists defend that position on moral grounds. So I don't think it makes sense to say you can't defend it on moral grounds. If it's not defended on moral grounds, then how?
Kant suggested that a key test for any ethical action is the question: what if everyone did the same? If we apply that test to pacifism, then the result is clear. If everyone acted as pacifists do, there would be no war. Would that be a good outcome? Realistically not everyone opposes war. Fascist intellectuals, such as they were, taught that wars are good for nations, and many businesses make good money from war. So not everyone would be pleased if there was no more war. But many ordinary people, the sort called on to fight, or their families, probably a majority of people, would consider the end of war to be a moral good.