The gist of it is that Stark has made the Avengers into a SHIELD replacement. My bet is something in the opening goes wrong, and compels him to distrust the other Avengers and try to replace them with Ultron or something. But who knows!
Hmmmm, that would tie into the "House Party Protocol" from IM3, if something or someone hijacked the armor(s).
Why? How? The theme is reinforced by the leak. The theme is reinforced by Cap personally taking down SHIELD/HYDRA's spying/drone apparatus. This is a movie that sides with Manning and Snowden against the CIA, drone strikes, and blind patriotism. I think that's enormously brave and powerful of them, and the movie as a whole forms cohesive social commentary about that stuff.
Because, just like the leak, it was based on, it won't stop, it never stops, heck I'm suprised that people are shocked by it really, more so those of us on the net know that everything they do, say, watch or capture on is being watched already, and that it will never stop. It's the times we live in, it's going to happen. Heck, Sharon went to work for the CIA right? they're into the very same things.
His trust in Fury was gone soon as he found out that Fury had his place bugged and that the girl he was trying to ask out was sent to watch over him. It would have made more sence to have that "this isn't freedom, it's fear" talk at the end of the movie, followed by a quick speech about how Fury likely knew WS was Bucky the whole time,. and that both men were being controlled by 'their' sides respectively, one by brainwashing and torture, the other with lies and deception,
then quit Shield.
Now be honest, you would have loved to hear it.