To address this point of the USO angle rallying the troops and inspiring the American public-
How exactly would this work? The troops will see some muscle freak on stage performing feats of strength and acrobatics that they couldn't possibly do. So if anything, they'd be discouraged by seeing Cap up there. They'd be thinking, "Why are they sending me into combat and not this super human clown?" However Cap on the battlefield would be inspiring for the troops.
As for the public- they'd look at Cap and think "this is where my tax dollars are going? why isn't this clearly able specimen out defending his country?" .
You're assuming that he'll be presented to the public as a real super soldier. What if he's not? A while ago in another thread I brought up the idea that, maybe, the government will be hiding him in the USO. Plain sight, so to speak. As far as anyone in the USO is concerned, he's just the guy that fit the costume. It's a long shot, sure, and probably wishful thinking on my part, but it's better than assuming the worst about a movie before we actually know anything about it.
As for the whole "the USO show isn't plain sight" arguement that was brought up last time, well, I think a person in the USO show can be hiding in plain sight. Plain sight does not equal discreet, as evidenced by comic book Tony Stark. Tony Stark built the Iron Man armor, and he was eyeball deep in the superhero and military worlds, and yet no one thought he could possibly be Iron Man. No one said "yeah, that guy's rich and famous, and he made the armor, he must be Iron Man!"
Not to mention that Cap is supposed to be a secret weapon. This s why he's in a MASK, using the codename Captain America. Putting him on display shows that the army could only produce one super soldier and also puts him in danger of assasination. If the Nazis could kill the scientist who developed the formula in a top secret locale, then they could get to Cap in public. .
Dressing him up in a costume, essentially painting a target on him, and putting him smack dab in the middle of a war zone won't increase his chances of being assassinated at all, right? If the Nazis could kill a scientist in a top secret locale, then they could pinpoint the guy in the red, white, and blue pajamas on the battlefield. And dressing him up in a costume wouldn't give the Nazis the impression that he's one of kind, would it? It's not like the government is giving everyone costumes just to boost troop morale.
The costume protects Steve Rogers, it doesn't protect Captain America. In fact, I would say it has as big or bigger a hand in creating the problems you pointed out above as the USO. And that's only if, in the USO, he's presented as a real super soldier, and one of a kind. If he's not presented as either, then what reason do the Nazis have to kill him?
The only way to ensure the above situations (assassination, the nazi's realizing he's one of a kind, etc.) never happen, or limit the chances that they would happen, would be to keep Steve locked up inside a secure facility and never let him out until you had a whole platoon of super soldiers. Even if you did let him fight, and didn't put him into a costume so he wouldn't garner extra attention, it would eventually become obvious to the Nazi's that there was this one guy that was extra special. Because no costume or secret identity or whatnot could ever hope to hide the fact that he's stronger and faster than an average human.
And his being on a USO stage merely to explain why he's in costume isn't very compelling.
And Captain America wearing a costume "just because" wouldn't be very compelling, either.
Why the hell do fanboys have such a problem with directors trying to make comic book movies something more than fun popcorn flicks? It's annyoing, moreso because most of the fanboys here probably spend half of their time complaining about plot holes, bad writing, and "Scooby-Doo villains" in other movies. Yet when directors try to avoid these things in superhero movies by adding details here and there, they complain about it. And why? Because it wasn't in the comics. Are people seriously telling me that they would rather have something NOT explained in a movie just because it wasn't fully/ever explained in the comics? And they would rather a dumb ass reason be used to explain something rather than a good one because the dumb ass reason was in the comics?
Please, if someone wants filmmakers to regurgitate the comics panel for panel onto the big screen, then I suggest they just keep on reading the comics and forget the movies. The movies will never be the same. And even the ones hailed as good adaptions of the comics aren't the same, it just that people learn to ignore/accept the changes because they enjoy the final product.
So, basically, I think people have to put their bias (it's got to be exactly like the comics or it will suck.....blah, blah, blah) aside for five minutes, and see how the USO idea plays out before they say it's going to doom the movie. We don't even know how far it's deviating from the comics yet. Yes, I know the USO idea wasn't in the comics and it's an obvious change, but you can change certain things in a story, and still preserve enough of the main elements to please the fans. I mean, Tony Stark didn't originally get injured in Afghanistan, and he didn't build an arc reactor, yet because he still got shrapnel near his heart and built a suit of armor to escape, and a man named Yinsen was there, people thought his movie origins were accurate enough, didn't they?

