Sort of disagree. The American people accepted intervention in Kosovo for the very same stated purpose: to stop genocide. Also agree that genocide is going on all over the world and we do nothing. But we apparently are willing to draw the line at genocide in Europe.
The reason for "sort of" disagreement: Germany in 1939 was no Kosovo. Armed to the teeth with superior might to ours (at the time...our military was gutted after WWI) I don't imagine Roosevelt could have succeeded in rallying the nation around invading Europe at huge cost (dollars and lives) on moral grounds alone. Today, he might.
No one asked the American people about it. I don't believe the whole story behind our intervention has been written. What was going on was certainly nasty but I don't think it deserves to be called genocide.
If the American government cared so much about genocide why didn't we intervene in Rwanda? That was an indisputable genocide.
But there our involvement was relatively minor. There would have been more opposition if there had been more US casualties.