Many advanced countries require people of a certain age to do a stint in the military.

I think a volunteer force is preferable to a conscripted force.

A volunteer force is definitely superior if you want to limit the concern of the general population about wars and make making war politically easier for the ruling class, which was a major consideration in the US switching to an all-volunteer force.

About 80+% of people join the military for money, college, and other benefits. The well-off people don't need the military for that. So, a volunteer military naturally selects for a make up of lower classes to be sent to die overseas to largely protect wealth of upper classes.

If there was a lottery, pushback from casualties would come from more people in upper classes that could cause real problems for politicians and generals. Could even be their own kids sent there. Switching to a "volunteer" military in an increasingly-shitty economy sweeps lots of their problems under the rug. ;)

A volunteer professional force is better prepared than one composed of essentially transient members, so casualty rates, should they need to enter battle should be lower than a conscripted military.

Yes, the fact that our military is more racially diverse than our general population is a reflection of our socioeconomic gaps. Ironically, blacks were initially excluded from the WW2 draft because "prejudiced questions about their ability to fight and worries that tensions between black and white servicemen might erupt." [0]

[0] http://www.americainwwii.com/articles/your-numbers-up/

Probably not one the USDS is particularly well-equipped to solve though.