Hugh, good for you for checking out the details on this new academic/ideology/history  center, and especially funny to find Will was a paid speaker at its opening!
In my view American history is a hodgepodge of the good and the bad, and if you want to ignore one Narrative you can make a great case for the other.
Will notes  "Because America is, as Lincoln said, dedicated to a proposition with far-radiating implications, ..." But George ignores WHAT that proposition was, Jefferson's "all men are created equal -with certain inalienable rights."
A wonderful sentiment, it's what made the US special, except for one very sad fact-- until Lincoln, that "equality" was  mostly intended only for white men.   Our history of slavery of African-Americans  and theft of Native American land is history, not some wild story cooked up by Charles Dalton or a wild-eyed Progressive sociologist.
We're now in a painful, awkward period trying to ensure that America's bounty is to be shared by all, thankfully.