Just to expand a little on redben’s point, a critical plank of this story line is that both sides of this argument have merit – it is not a story of heroes versus villains, but of two sets of (on balance at least) good people who are divided by a pretty thorny ethical and ideological issue where there is no obvious bright line between the right and wrong answer.

As you say, Cap is very much of the opinion that individual freedom cannot be sacrificed for security, and feels that it is wrong that people should be under the scrutiny and control of the government not for what they have done, but for who they are and what they might be capable of doing one day. He feels that the government is not necessarily a safe enough pair of hands to hold such power. All of this strikes a chord with many people and resonates with much recent history; the concerns embodied by that character are all legitimate and echo real world issues of the proper balance between personal freedom and collective security.

At the same time, Iron Man represents an equally fundamental question, one of democratic accountability that can be expressed in a form of words familiar from an unrelated by highly revered comic franchise; who watches the watchmen?

You have these individuals of exceptional power and ability who have set themselves up as the protectors of the planet. They are terribly heroic and all, but they were brought together by a high ranking operative of a covert intelligence agency who didn’t even have the authority of his own organisation, acting without the support of the other Shield Council members, and that organisation itself was subsequently discovered to be fatally compromised.

Imagine how we would feel if a senior spook in the NSA, CIA, or MI5 just turned around one day and announced that they had taken it upon themselves to create and unleash a ‘contingency team’ equipped with next generation military technology unlike anything seen before (don’t worry about funding, where the tech comes from, or other practicalities – just run with the idea) in order to ‘maintain peace and security around the world’ without any civilian oversight and indeed without actually bothering to consult anyone first, including their own government? Imagine if then the organisation that person worked for transpired to secretly have been extensively infiltrated by neo-nazis. Serious questions would have to be asked about how this happened and if this organisation, or the team it created, has any legitimate authority to act at all. Just determining what the team’s status under domestic and international law would be at all would be headache.

Now further imagine that one of those operatives turned around and essentially said “states and democratically elected governments can’t put limits on me and my team because that undermines our freedom. We have the power to unleash mass devastation but that is OK because we are the good guys. You know that because we fought the bad guys, and nobody who fights your enemy could ever be a threat to you in their turn, right? When has that ever happened in history…? Oh, and you can’t arrest this multiple murder and known terrorist because he is my buddy. It wasn’t really his fault – he was brainwashed into doing it but he is better now. I have no proof or anything, just trust me. You know you can trust the guy who works entirely outside the democratic system of accountability and military chain of command, and about whom you don’t actually know very much at all – what could possibly go wrong?”

This movie’s plot line addresses the point that the Avengers run around unleashing large scale destruction in the name of saving humanity without even a smidgen of an actual legal or democratic mandate to do so. Calling yourselves ‘the Earth’s mightiest heroes’ doesn’t just afford you carte blanche to do whatever it is you believe you need to without reckoning the consequences, and Tony knows that better than most after Age of Ultron when his own intellectual vanity, tendency toward taking risky short cuts, and desperate need for control unleashed a major threat upon the world.

The point Tony represents here is that individual freedom must stop at the point when it starts to impinge upon the freedom of others, and when you possess the kind of power the Avengers are depicted as having, paired with the willingness to use that power at your own discretion while deferring to no other authority, your actions will inevitably impinge upon the freedoms of others, and if you refuse to acknowledge that or accept any limits upon your range of action then you start to look less and less like the noble hero and more and more like a fairly villainous type who in practical terms lives by a ‘might makes right’ philosophy even if you don’t openly espouse one. At the very least it gives people an entirely legitimate basis on which to question your agenda.

Again, these are valid points that relate back to contemporary concerns about the ways in which security is provided and the powers we confer upon covert organisations to protect us from threats that we are largely left in ignorance of.

While it may be easier to empathise with Cap’s point of view out of the gate than Tony’s – mostly because it fits more easily into our dominant social narrative that places a high premium upon personal autonomy and venerates the idea of the hero as a moral paragon taking on the corrupt system – when you think about it for a bit both perspectives are wholly valid (the lone hero following their own flawless conscience can easily also be read as the rouge operative taking it upon themselves to make decisions for all with no right to do so, depending upon context), which offers a very interesting and promising set up for the movie.