As the song's lyrics go, "You don't tug on Superman's cape..." inferring that once should not trounce American heroic icons.
"Batman v. Superman" and "Captain America Civil War" goes where no cinematic hero storyline has gone before, especially during times of aggression against the United States. Both films have - like X Men beforehand - ruffle the Spandex of heroes by categorizing them as "weapons" that potentially upset the balance of power. The DC and Marvel universes have favored democracy and their actions stemmed from defensive postures. Note that "Civil War" stems from a Marvel story arc in 2006.
However, super beings loyal only to one country does ignite a quandary: Do other countries such as China or North Korea have any super beings?
Civil War has Captain America, Black Widow, Scarlet Witch and The Falcon, who have confronted a super villain in Lagos, where the Witch tries to displace the blast of a suicide bomber into the sky with telekinesis. Collateral damage destroys a nearby structure killing Wakandan humanitarian workers. (recognize the similarity to Superman's rescue of Lois Lane setting off collateral damage.) As a result, the United Nations wants the Avengers, i.e. super beings, under oversight control of the members. Captain America refuses but Iron Man supports the so-called accord. The super hero team splits.
"Batman v. Superman" more concisely states the daunting question - one nation with a supporter such as Superman, who has the powers of a god, upsets the defensive balance of the world. Assuming Superman, the Avengers or mutants are 'on duty,' they have the capability to stop (or start) theoretically any human force. They overpower nukes. What prevents them from crowning themselves king, dictator, or whatever, and ruling the world? Their powers are used for good, but what if one succumbs to lust, greed or an ailment such as the brainwashed Bucky Barnes, whose defection could symbolically relate to a way of calling attention to PTSD.
Stretching this thesis, Superman has a love for Lois Lane and her safety could turn into extortion by terrorists (or others) to compel him to destroy and kill. Same for the Marvel universe.
Comics and movies have rescues in a nick of time, but they also include main street battles with monsters, aliens or others in which the infrastructure of the city receives more damage than Hiroshima. No one has asked, who pays to clean up and rebuild?
Essentially, it's a 'natural disaster,' compelling the government to clear the war damage. Had the battle(s) not been fought, the planet or nation would have been destroyed. Right?
Beings in Stan Lee's Marvel Universe received depth of personality development, meaning they showed emotion, unlike rival D.C. characters who only showed slight personal ripples maintaining their secret identities.
So, would the Sokovia Accords have told heroes when to use their powers? What stops them from, well, going independent? Is there a put-it-back-like-you-found-it clause?
Additionally, what's 'fairness' crosses national boundaries and reverts to the eyes of the beholder. Truth, justice and the American way (which opened the George Reeves Superman TV series) would not fly (pun intended) in Germany, Japan or Russia?
Ironically, Japan has an edge in its science fiction nerdy reliance on their own animated heroes serving as role models. Think Astro Boy, Sailor Moon and Goku battling Supergirl, Thor and Flash. Russia would pit Major Thunder, Demon Chaser and Red Fury versus Hulk, Spider-Man, and Scarlet Witch.
Japan's animated legacies have not yet achieved global big screen, tent-pole treatment. So for the American heroes and studio bosses, the hundreds of millions in costs for making these heroes fly and cities and bridges fall have prompted film studios to consider international sensitivities in a production. They don't want to have their blockbuster banned in a country where they need the box office revenues from foreign cinemas to turn a profit and accumulate wealth for the next installment.
You know something? I forgot the various universes of super-villains that counteract the heroes. Joker. Catwoman. Enchantress. Harley Quinn. Lex. Mystique. Octopus. Let the 'bars cannot hold them' Legion of Doom, Masters of Evil, and Suicide Squad offset any U.N. accord.
And to use Stan Lee's immortal words, 'nuff said.