Dire Bare
Legend
Remember, Rush said the Sgt. was not the kind of guy that he'd have approved...and that he (Rush) was part of the personnel approval committee. To me, that says "Sgt. Angry" was placed on the base for a particular reason by a particular person in one of the agencies or gov't branches overseeing the Stargate program. Assassin? Spy? Saboteur? Psych experiment?
Well, Greer (Sgt. Angry) was in the brig during the attack on the base. He was only let out because to leave him there would condemn him to die. And now, Commander Young has limited resources and must rely on those he has available. Young and Scott (Sgt "I have a weepy past") seem to trust him. And really, they haven't had a lot of time to sort everything out yet, and there was the whole, "We're gonna die from lack of air" thing going on . . .
Methinks that Greer is basically a good guy, but has anger issues . . .
I doubt there is a conspiracy of sorts behind Greer being at Icarus Base. I think it's much more simple, we aren't being given idealized versions of military characters in the new Stargate, but rather more realistic portrayals . . . which means flaws . . .