It seems to me that people are just assuming that because Banner was able to direct the Hulk in a single battle against a common enemy, he is all of a sudden a giant green boyscout.
It was one transformation that followed hard on the heels of the Hulk rampaging on the helicarrier almost killing BW and putting a whoopin on Thor. Yes Loki released the beast but after that, the Hulk just did what Hulk does . . . SMASH! I'm pretty sure BW and Thor wont be high-fiving the Hulk anytime soon.
Well if you want to disregard TIH and the Hellicarrier sequence, yeah, he's a great guy. However even when he was in a "controlled state" in the comics, teammates and friends were still wary of when the Hulk might bust loose again. It created a barrier which prevented the character from being fully embraced in any team.
THE most compelling aspect of the character is the struggle with the inner-monster. Yes, he was cast in a more heroic light in the Avengers but the underlying theme was that Shield and his teammates were concerned and uncertain of his stability. Not including these conflicts is essentially neutering the chaotic nature of the character and removing a potentially dynamic story element.
It's not like General Ross went away or anything. One uncontrolled transformation brought on by pain, fear or rage and some collatoral damage (the Hulk's bread and butter) would be sufficient to start the hunt again.
I say make the Hulk an antagonist is the next Avengers! The Hulk CANNOT be controlled. Directed yes. Controlled NO WAY. Furthermore, the Hulk does not WANT to be controlled.
I am not saying to make him evil, I am saying make him the Hulk.
Those saying the GA wouldn't accept the Hulk in an antagonistic role, need to look back at the boards when people said the GA wouldn't accept the fantasy of Thor or aliens in The Avengers.
The incredible success of The Avengers, that interwove SO many varied scifi and fantasy elements in a single movie, proves that there isn't a lot that the GA wont accept if adapted well.