it's not "blanket approval"..it's something many have thought through and agree with..you still didn't answer what's wrong with introducing to kids the idea of American exceptionalism, something a french thinker observed when travelled to the US and wrote a book about, how different this country was back then compared the rest of the World, where many original concepts and values had been created, and how it paved the way for so many opportunities for people regardless of their background..
I think that people who subscribe to liberal views don't truly understand the role of the US in the World's history, the foundations on which it was built and why it has become so successful..that's why they'd support any changes to this country left and right, even if it'd change the very foundation of it...and they don't appreciate the opportunities this country has given them, more fascinated with themselves than with the country..