I prefer Danr's explenation.
But think of this.. the guy in the bar from WC4, who get's taken hostage and tortured by seether in the "bad" path is one of those guys who had nothing, and the military offered him food, a roof over his head, and something to do, when that was gone he went boozing and became a drifter. He started out as a gunner, and worked his way up to pilot when they(confed) needed pilots.. He went to BW because they offered him thesame.
Dallas was pretty much born with a silver spoon in his mouth, IIRC, and he just wanted the glory and credits. Without a war to fight, he could just breeze through military service, come home a "hero".
With the exception of the mexican guy from Academy, Vaquero, Cobra and Vagabond all pilots(of wich you know the background) you fly with seem to be born in upper-class families or have a family line in the military.