First if you take people out of the economy cuz their serving there will be more jobs open because the public demand would not change.
In order to clothe, feed, train etc the additional soldiers the fed govt would need to spend money which would help spur the economy.
While in the army people recieve training beyond just shooting. After 18-24 months someone may have worked as a mechanic, paramedic, electronics maintainance, or tons of other skills that would be of use to them in the private sector. They can now get a job doing what they were doing in the service.
By serving people would probably have a greater sense that they are part of the country. Having served you feel more that it is your country. I am 99% sure you need at least a GED to serve and if there was a conscription policy (aka draft) many people who don't have a high school diploma or GED would be able to get one probably paid for by the govt.
Our current army is a few million if you add a draft the size will increase and that will help serve the national interest of security like in the Constituion where it says "provide for the common defense"
If we had a draft and bigger army, maybe we could have had more people in national guard and state guards to help with national disasters such as Hurricane Katrina
Also, you might want to take about state service instead of just military. By this I mean maybe you can say that if people don't want to be in the navy, army, etc they can work for the parks depts or the immigration service. This would also give them skills and it would be able to allow people who object to the military to still fulfill thier time to the govt.
Thesis possibility- Military service in the United States should be compulsory (reqd) because it will provide economic and social benefits to those people who are serving as well as create a benefit for the general public as well as nation as a whole.
