You can guarantee that if civil or military service is required, there will be a huge number of metrosexuals, homosexuals, transsexuals, and just plain perverts forced into the military. Not to mention the worthless turds who are either drunk or on drugs or so screwed up, you would have to assign one person per idiot just to make sure they didn’t permanently damage an expensive piece of equipment or kill someone through shoddy work or carelessness.
Then throw the worthless ones out with a bad discharge that follows them through life. If military service is mandatory there won’t be any need to keep the ones that are lazy, dangerous, or undesirable.
And homosexuals can opt out just by declaring their preference.