Well what alot of people dont know is the background story to space above and beyond.
It was deep, and everything happend for a reason.
http://en.wikipedia.org/wiki/Space:_Above_and_BeyondCheck it out, unfortunitly i cannot find the more detailed storyline. :|
Basics are, between being unable to make babys, then the A.I. wars, then the chig wars (and all the multiple war on earth before during and after), yeah humans in S.O.A.B. was on the nitty gritty, to say the least.
Wildcards were all invitros "genetic engineered humans, not* clones" they were slaves of state and therefor were not treated as humasn, they have no family,no sisters no brothers, so when the human A.I wars kicked off, most would sit the battle's out, and through that became seen as lazy worthless and just downright not caring, about anything.
After the A.I. wars, they were freed, and thus had the ability to join in the military.
But the "tank" stigma still fallows them.