Ah, I see... I didn't infer any of that, and I agree that it isn't satisfactory as an explanation. Bruce never gives the impression that he can control "the other guy" to any degree at all, before that last instance of hulking out; Bruce is always shown as completely horrified of him, and willing to do anything at all to prevent the Hulk from appearing again. The Hulk is always presented as a catastrophe, something that must inevitably cause incredible destruction. This all seems far too extreme if Bruce actually *can* control him under normal circumstances.

It also makes SHIELD's countermeasures for the Hulk more suspect, because it tips their motivations over into "we don't trust anyone who controls such power and routinely devise methods to take them down" territory, where before it's merely been "we must guard against the worst-case-scenario of an uncontrollable, destructive force appearing".

That's not to say that your friends' interpretation isn't the intended one. I find it entirely possible that it is. This is the fourth different explanation I've heard for The Hulk Plot Problem, though; very many viewers are trying to find an explanation because they thought things didn't add up. So really, whatever was meant to be the explanation, it should definitely have been made clearer in the movie.