There is very little difference between arms and modern industrial chemicals. Without arms, we can still kill large populations by destroying their water supplies and crops. Even if you managed to rid the world of every weapon more advanced than a knife, if/when conflict arises, we can kill populations at a grander scale than ever before.

He is is making the correct assumption that even if some people want peace others will be more than happy to kill you and rationalise that it was actually a good thing. So you are both right: the alternative is peace or war. I would definitely prepare for war though. To do otherwise is naive and gratuitously stupid.

Si vis pacem, para bellum may be a practical advice, but the outcome of it is an arms race. Which is a big problem, because that feedback loop ties up resources and manpower that could be better used elsewhere. So even if it is the most practical option now (since we don't have a single global government), we need to recognize how shitty it is and maybe figure out how to reduce its impact.