The problem is that we need to for many reasons transition to an international order of democratic cooperation instead of economic and military domination. And if the US can never accept this kind of shared and cooperative approach foreign policy of everyone is going to be forever dragged towards this kind of zero sum bullshit we have at the moment. Even though it's obvious that foreign policy doesn't have to be zero sum.
Even if other countries are potentially less honest with their implementation of global treaties, even a relatively slow movement there and maybe a more thorough movement in the US makes everyone better off.
The only way to actually foster a cooperative relationship is to make yourself vulnerable, otherwise it's just coercion and power not cooperation. And yes if you get hurt too much maybe you'll have to leave again, but this pessimistic outlook from the get go is certainly never going to lead to the changes we obviously need.
How do we solve things that require global attentio and accountability, like climate change, with an increasingly hostile and isolationist country calling the shots on decisions about global economic matters.
Simply put if I want to live in a world somewhat resembling the current one in 60 years, American collapse or integration into global democracy is a necessity.
Also calling a country that has been at war for 80+% of it's history a protector of global peace seems a bit questionable. Similarly I don't think anyone can conclusively say that the US has done more or less harm than good. But by that same nebulous metric shouldn't China hold that same title, as well as the Soviets, the British empire, the Spanish empire,the Romans ?
I would expect almost everyone to feel more ambiguously about the later list than the US, but both the US and empires of the past are exactly what they've always been, a tool for those inside, especially the ones in power to increase their quality of life, while everyone outside gets to be exploited, integrated, subjected to rules that do harm, and be attacked, regime changed and so on. It's not actually the US that is a problem it's the US being a modern empire that's the problem.
That the US tries to be a liberal democracy doesn't really lessen it's status as an empire, especially if the powers at be largely prevent it's people to decide against the status quo of domination.
Almost by necessity the most powerful are the most harmful if there are no systems to prevent their harm, diffuse their power etc.
Don't you also have both ?; Escaping to an aggrandized past for dread of the future and daydreaming about an idealized future self to wash over past shortcomings.