Should've used the gamma desert explosion origin?

Well, they can't use it for multiple reasons, and even Ang Lee addressed that on the commentary for the film. Basically, the reason why there was never a comic book accurate origin for a Hulk in live-action is because the origin of Hulk is outdated. And, as I think, because it's also very questionable from a moral standpoint. First, Hulk's origin was relevant during 60's, during mass hysteria about nuclear war. Second problem is the moral problem. So Bruce Banner is a do-gooder scientist who became a victim of the genetic mutation, who can't control himself during the emotional stress, which turns him into a giant monster. We have to sympathize with him. But when you think about it... So he was trying to create a nuclear weapon for the army, right? A weapon that would most likely be used, I dunno, to kill thousands and thousands of people? So when you think about that, you kinda lose sympathy for the character, since he wasn't really creating that gamma bomb for peaceful reasons. He knew that it would be used for the destructive deeds.