Ok so I saw another weird theory about why Steve and Tony were fighting on the helicarrier and I would like to reiterate:
The mind stone was influencing everyone in the helicarrier lab and here's why
First, before we get knee deep into this, let's break it down piece by piece. We know, from aou and the avengers 1, that the mind stone does many things.
1. Makes people wildly suggestible (Clint and selvig)
2. (If you believe as I do that Loki was in some way influenced as well) can steer people towards certain actions that they might not necessarily take on their own, while still allowing free will
3. Makes people see their worst nightmares (Tony with the space whale, then later Wanda, a product of the mind stone, with everyone)
4. Can be used to send people (the hulk) into a mindless rage (again through Wanda, but I'll get to that)
5. Creates a humanity-hating robot (Ultron)
All that, among other things, but those seem to be the main points there. And so, if we were to sum all of that up, it seems to have the ability to be inflammatory when it comes to people's higher functioning and thoughts. It has the ability to lower people's capacity for logic and critical thinking, at the very least.
And now the scene(s) in question:
In summary, characters cycle through the lab at various points in time. Bruce and Tony spend the most time in there, followed by Steve, then Natasha and Fury and Thor together. The more people in the room, the more chaos ensues.
When it's just Bruce and Tony, there's friction yes, but keep in mind that Tony has been thoroughly schooled probably from a very young age on how to keep his emotions in check (esp in front of important people and the media) and Bruce tells us himself later on that he's always angry and he can deal with it very well.
Steve, however, has always been a man of emotion and that's always helped his cause, so he lets his heart lead him everywhere. So, when he feels any sort of annoyance, he lashes out because that's what he's always done. Tony makes a joke (something that we see Bucky did often in stressful situations) and he immediately gets stern and almost fatherly (an interesting description in itself, since he's almost exactly Tony's father's age in a way, but that's an essay in itself). When he hears Tony's doing something not exactly above board (which Steve himself has done so many times they've made three movies about it), he cracks down again despite doing the exact same thing in his own way two seconds later.
All things considered, everything Steve said there was pretty out of character for him given what we've seen of him before and since.
The kicker then comes when everyone's in the room. Those skilled the most in emotional control (Natasha and Bruce) stay clam throughout most of it. The rest of them get their emotions turned up to 11
Tony, who normally is very good at acting to get exactly what he wants, is caught off guard by the presence of his father's hero ("that's the guy my dad never shut up about?") and therefore conflates feelings of his father with feelings of Steve, childishly lashes out.
Steve, who has been consistently called Captain and has the most military experience out of anyone besides Fury (who is already on thin ice with him, probably, since he's lied about everything since they met), acts as a stern commanding officer figure and funnels all his emotion into that anger. (He also only really knows one person here minus Fury, in a way, and has latched onto Tony as his anchor to the past since, in his eyes, he acts exactly like Howard who was always a blase charmer that was too in his own head to seriously think about anyone else) (also all he knows about Tony comes from his work with Howard and Natasha's assessment when Tony was dying and trying to give up his responsibility so there would be people there to take care of things when he was gone, which to Natasha looked like him being selfish and giving up)
Fury, feeling on the back foot here since he's used to holding all the secrets and not being found out like this, shifts blame, turns on everyone else, tries to push the attention in every other direction.
Thor, a crowned Prince of a world much more advanced, makes himself seem higher than the rest, looking down on them, painting them as "petty"
Then we get the shot of the scepter behind them all, curved over them like an umbrella, encompassing them all.
The scepter plays with people's emotions, plays up their base feelings and overshadows logic and higher level thinking. It enslaves them all to whatever emotion they're feeling, without concern for others.
Then, in all the chaos, Bruce slips. He gets distracted. Everyone's eyes are on him (when we've seen him when he first got inside the helicarrier actively avoid being noticed and shying away from attention) and he's being pushed to talk about things he very much doesn't want to. His control lapses, for just a moment, and the scepter gets its chance.
We know from aou that it's sentient, it thinks and it's interference is finally paying off. It gets Bruce on the defensive, losing control over the situation, so close to the scepter, and so it reaches out. Bruce gets pulled in. He picks it up, unconsciously. He's ready to hulk the fuck out.
And then they find the tesseract and the explosion happens and Bruce, still preoccupied with how they intended to kill him if he got out of line, is told that Natasha is getting her life, which was safe in the first place while he was one wrong move from being out down like a dog at any moment, and he hulks out anyway.
Now we all know the rest. And so, as you can see, the scepter was messing with them, pulling out their more volcanic emotions, pushing and pulling them in every which direction to get someone to use it's power, like they do in aou.
So, if you really break it down, it's easy to see that the reason for the big fight wasn't just big personalities:
The mind stone was fucking with them, and having that interaction be the basis for the team for the rest of the movies is why it all goes pear shaped at every opportunity
(the only reason they don't completely fall apart every second is Clint, actually, but that's an essay for another time)















