Nitpick - in Starship Troopers, those who satisfactorily complete their term of service may vote, hold office (i.e. be elected), and hold certain jobs such as police or teacher of political history.

The majority do their service in any one of hundreds of civilian roles. Only a tiny percentage do it as military service, and of those again a tiny minority hold combat positions.

That it is only military veterans that are allowed to vote is a misconception due to Verhoeven's movie. The book explicitly points out that veterans are no more a better person than any other when it comes to crime, unemployment, et c - the only difference is that they volunteered to serve, out of their own free will, the greater good of the collective above their own personal leisure or desire or profit.