@"America is one of the main sources of international war and instability. The world would be much better off if America just fucked off and stopped interfering like the imperialist 19th century power it still thinks it is."
The mistake is in thinking someone else wouldn't take America's place if they 'fucked off' - look at Syria, the US considered sending in ground troops, and rejected it. What happened, Russia got involved, Turkey, Saudi Arabia, Hezzbollah and Possibly Iran, all have some involvement.
The US not acting like an Imperial power isn't a magic recipe for peace. The UN is a joke, and Having the US become an isolationist power (like most Libertarians dream) will not end well.
It will result in instability in many former US allies as the balance of power shifts. China vs Japan for regional control in east asia, Turkey, Saudi, Israel, Iran and Egypt all ightin over the middle east. Pakistan and Afghanistan, broadly messy south american nations, South Korea.
All while Russia and probably the UK and France decide they want to fill the void left by the US.