I’m paraphrasing, but the reason the duty had to be somewhat hazardous (according to Heinlein) is to proove you would put the good of society ahead of yourself (a good test for politicians-if it sticks). They also accepted non-military service but given the subject of the book there wasn’t as much detail given to those positions.
The main difference is in the government itself. The government served society, not the other way around.
sounds like society serving government to me