Calling on private capital to make risky investments in new technologies that only have one likely customer - the US government (well, maybe some Third World petrodollar recycling options, who knows) - seems to avoid discussing how the current gigantic military government budget is being spent.
Fundamentally, military expenditures don't have much in the way of additional positive economic effects. Say you're producing construction cranes, for example - each crane facilitates further economic activity, in building projects. If you're producing tanks - well, unless your economic model is to raid other countries for raw resources, it's not going to have that same effect. There's also little likelihood for a large consumer market for your product.