Developing it was probaly a great revenue earner for the defence contractors, but wouldn't it have been better to spend the money on improving the domestic infrastructure in the US, and in encouraging the purchase of US manufactured products.
The United States has been known to be the most exorbitant spenders on military hardware (Aircraft carriers, Fighter Jets etc) and other developmental ventures. But the products developed by the US have a technological edge and led to the invention of many newer technologies. While one can debate over cost to advantage ratio, I would say we all believe that military hardware from the US is much costlier than those developed by other countries.
The US defense manufacturing industry is private and has huge lobbying power in the Senate. They can extract huge budgets for developing technology and extracting profit. The entire American legislative process is very susceptible to lobbying and industrial groups exert tremendous resources and force to swing the tide in their way. Plus they regularly need to distract their population away from real issues using war. War and other conflicts allow the populace to have that nationalism feeling which keeps the entire democratic machinery going and the people willing to pay their taxes and fulfil other obligations towards their nation.