> the US has been a country founded on immigration and racial diversity

This is a misreading of pre-1965 history with respect to immigration. The Naturalization Act of 1790 explicitly states:

"any Alien being a free white person, who shall have resided within the limits and under the jurisdiction of the United States for the term of two years, may be admitted to become a citizen thereof... making proof to the satisfaction of such Court, that he is a person of good character."

So the "diversity is our strength" slogan is a modern invention and an attempt to retcon our history.