Can US walk out of this role it plays, and still remain in a beneficial position? This is the biggest raging debate in the US right now. You can check the works of Peter Zeihan (who claims that US dollar will become even more desirable after the US walkout), or Brent Johnson (who claims that, even in a complete decline scenario, US dollar will still maintain its dominance above and beyond everyone).
Either way, Americans are hugely divided on maintaining this world order as it exists, and saying "you guys would lose so much without this", it's just taking a side on that debate.