Defense spending also goes into R&D which, depending on the product, can be translated to commercial goods. Warfare is the leading motivator of technological advancement after all.
Of course, that's just a little devil's advocate right there. Research is great, but makes up a minuscule part of the budget.
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[witty phrase including the guru champ SuperNiceDog]
If there is one thing I know, it is that I know nothing.