The difference is that, in World War 2, Germany was reduced to rubble and a significant fraction of its population was killed off because of the direction that its society took. This forced it to take a really long and hard look at itself and figure out what it could do to make sure that this never happened again.

By contrast, the U.S. has never been put in an equivalent position. The bloodiest war in our history was actually the U.S. Civil War in the 1860's over slavery (and some other things, but mostly slavery). Although the anti-slavery North in that war won and was able to successfully end slavery in the entire country, racism itself was a whole separate issue, and (simplifying the history a bit) it continued to exist formally as a less extreme government-backed institution until the mid-20th century. (An example of this were the "separate but equal" schools that segregated black children from white children and were very much not equal.)

Of course, this only changed the law of the land, not hearts and minds. Education is very local, so there is no central authority which makes decisions about these things, and people regardless have the option of sending their children to private (often religious) schools, or even to home-school them. Furthermore, unlike many countries, we take freedom of belief extremely seriously, and additionally we extend this to a near-absolute freedom for parents to teach whatever things they want to their children to believe. The U.S. stance is essentially that we might not like the values that our neighbor is teaching our children, but we like the idea of the government telling us what values we are required to teach to our children even less, and this is essentially because our country was founded on a fundamental distrust of government and this general attitude has propagated down the generations.

So, what would it take for the entire country--and remember that this is a huge and incredibly diverse country--to get together and decide that we really need to, collectively, put aside our own individual opinions of what our values should be and what we should be teaching our children and refashion our entire society around a new collectively held set of values? That is asking a lot of people, so probably the most likely way that would get done is if fascism takes over our country and drives us to start a war that results in the entire country being reduced to rubble and a significant fraction of our population being killed off. This would force us to really take a long and hard look at ourselves and figure out what we could do to make sure that this never happened again.

(Except that now that nuclear weapons exist, "rubble" takes on a new meaning, so that rebuilding part may not get a chance to happen...)