Do watch Sargon's video.
MY BRILLIANT OBSERVATION OF THE PROBLEM:
Technically meritocratic, but one thing people are too PC to point out is that who it really invites.
From the book: A "blind paraplegic" can be enlisted to count the hairs on a caterpillar by touch. Totally useless work, yet after two years he or she can vote.
Virtually all seriously disabled people will enlist, while a lot of able folks will choose the civilian life. Then the disabled vote themselves and other disabled welfare from the public largesse. Sound familiar?
To be totally un-PC, while in a "democracy" only half the people making the decisions are "below average" (as I heard a flaming liberal put it after the 2004 election), in Heinlein's idea, MOST of the people who make the decisions will end up being that.
Sargon's reaction to a bleeding-heart analysis: