The Avengers came together for a noble goal and did good work--Still do good work on our own. But a damn lot of that work was scraping for autonomy from SHIELD or the World Security Council or other groups of men and women who act in immediate self-interest and financial convenience.
Tony decided it would be best if we hand our reigns over to another one like another sort of arms deal. He meant well enough, probably, wanting to limit collateral damage, but we're people, not weapons and that's not the way our fight works.