It makes perfect sense if you put the context of the time, coming out of a truly crippling economic disaster, not wanting to risk going back again or loosing what was built up, those citizens felt ripped off by WW1, they lost men and money fighting a European war, America was not meant to protect freedom around the globe but only within their own country, they felt that by going to war and millitarising they would be sacrificing their freedoms at home for no good cause, they had little problem letting the Europeans sort their war out and deal with whomever came out on top (mind you this was the isolationists and not the administration, there was support for Britain well before the US declared war on the Axis). The paralells between the America First movement of yesteryear and many quarters today is astonishing.
Ultimately it was by going into Europe that America secured dominance, it's casualties in the Western European theatre and N-Africa were smaller compared to the Russians and they gained a lot more (untouched industrial base at home, gained control of W-Europe compared to the Soviet Union which rallied its base but lost some millions of lives for some impressive but still costly territorial gains across Eastern Europe). The Pacific was a solid set of gains; used atomic weapons and probably prevented the Soviet Union making unreasonable demands within Europe they did gain Japan and it was moulded to be a solid ally and buffer in many ways but China fell to the communists and within the decade Korea was an issue, and then down the line Vietnam as well (considering that the US did not give support to Ho Chi Minh against the Vichy French during the war and then backed the French against the communists pretty quickly after the war).
It is a very interesting piece of America built from it's immigrant populations (the German American Bund comes to mind) as well as good old fashioned isolationists who felt it was the best way to keep America's interests closed off and not to put themselves at risk for the sake of others (think of Pat Buchanan today). I certainly think that the world is a lot safer with America engaging and not being isolationist, some would disagree and argue that the US is no better than the USSR and that it's freedoms are simply illusions, and then their lines of argument eventually create a faux moral equivalence that justifies abandoning a fight against radical Islam or to simple blame America for the problem. In the end many isolationist attitudes existed back then and they exists today - tempered by the experience of Vietnam - history judged the attitudes in the 1930's by these groups poorly and I wonder how todays attitudes will be reflected upon.
