Military spending is bad for the economy. Because it is capital-intensive, what's made in the US doesn't create very many jobs. Parts and assembly are frequently outsourced and most of the arms exported to other countries are built at least in part in those countries as part of the purchase deals.
But a deeper and more pernicious problem is that military spending and weapons production drain the economy of its most highly skilled labor force, capital, and high-tech processes and product. Engineers and mathematicians at the top of their class want intellectual challenge--and a high salary to pay off student loans. Military contractors offer both.
Capital and money, but even more, machine and machine tooling capacity, are also drained from the economy by the arms industry. The Pentagon orders and pays for priority delivery of the best. In the process, the Pentagon is driving up the cost of these capital goods and limiting the productive competence of commercial industry. And of course weapons manufacturers absorb capital investment that could be driving new energy efficient or medical or transportation industry.
High tech processes run from software to paint application methods, and product examples include composite materials (thin sheets of fabric glued together to make airplane bodies), fighter plane windshield wipers that function at 1000 mph, oxygen delivery valves in fighter pilot suits. Investment in these narrow applications, the stockpile of patents shelved because the firms have no interest in commercial applications, and the top secret stamp on research all inhibit development of better coal exhaust scrubbers, photovoltaic cells, nursing home oxygen tank...