"Don't be proud of your ancestry goy!!!"

This is a very convenient way of thinking when your ancestors are entirely irrelevant to the development of America and when they were all slaves to Turks, Arabs, Romans, Egyptians and Persians.
It's very useful when the most infamous thing your people have done is get put into a giant concentration camp and killed like fish in a bucket by Jews.

It's also useful to stop Anglo-Americans (or White Americans) from defending the capital and institutions they ought to inherit through birth-right from foreign interlopers and their ethnic mafias.

Something that they were doing for literally all of U.S history up until the late 60's.