There's a weird phenomenon in U.S. political system where it's much easier to get spending approved by congress/voters if it's classified as "military". Thus many things that could be civilian projects end up as military.
That is part of the reason I think this stance is so admirable and interesting. I do not think defense spending is inherently negative. But even for those who do believe that in a strong way, I think it would be hard to leave those opportunities on the table and walk away.
Furthermore, he warned "Yet, in holding scientific research and discovery in respect, as we should, we must also be alert to the equal and opposite danger that public policy could itself become the captive of a scientifictechnological elite."