Say if the axis had defeated the UK and USSR. The combined power of the German, Italian, Japanese, British and French navies would have crushed the USA's control of the North Atlantic and the Pacific and possibly left the way open for an invasion by axis troops. Their isolationism could have cost them their independence.
But yeah your second point is valid. Presidents like Kennedy weren't interested in propping up or bringing down foreign governments, only preserving the peace and defending their allies. It's a few select presidents that ruined the USA internationally, and the paranoia of Communism and the almost blindness of post-war Americans that America was the only country in the world with freedom, and that you needed to spread this ideology. Your involvement in the second war was a good thing for the world and for America, although I believe your actions after it let the USA down.
Britain should have never have been forced to repay the lend lease debts for a start, it was economically ruined after the war like Germany - which did not pay anything for its actions. And although many call the Marshall aid plan a great donation by the American people, it was in reality a ploy by Truman to generate a market for American goods in Europe, to further US gains - not as is perceived to
entirely help a ruined Europe rebuild itself.
Also yeah Winston Churchill was a bit of a warmonger individual, but if Churchill was listened to in the first place there would have been no second war
. He was what the allies or rather Britain and the Empire, in the darkest days of 1940 and 1941 needed - a truly great politician and statesmen. Probably the greatest wartime leader the world has ever known.
The US needs more presidents like Roosavelt and Kennedy
. And less Republican morons.