"And the success of Desi Arnaz doesn't really say much. Louis Armstrong was also popular in the past, but that didn't mean anti-black sentiments and anti-black laws didn't exist."
The bottom line is that discrimination against blacks in American history was radically harsher than against anybody else, with the exception of American Indians (and the discrimination there was quite different, so it's hard to make an apples to apples comparison between blacks and Indians).
* I realize that there are a huge number of people who simply don't know enough facts to tell when I'm joking or not, and thus would get confused and disturbed when I switch back and forth between factual and facetious without warning. Fortunately, most of them don't bother trying to read me.
To recount: James Jesus Angleton's mother was Mexican and he was the head of counter-intelligence at the CIA for decades. When Robert De Niro directed a fictionalized biopic of Angleton's life, with Matt Damon as the Angleton character, the whole half-Mexican part was dropped, presumably as being too confusing to modern prejudices, and Damon played the lead as the most boring WASP in the history of boring WASPs.
Mel Ferrer, a moderately successful movie star of Cuban and Irish descent, was married to the exquisite Audrey Hepburn from 1954-1968.
Puerto Rican-born Jose Ferrer (no close relation to Mel) was a prestigious actor, winning the Tony and Oscar for Cyrano de Bergerac after WWII. He married white women five times, including George Clooney's aunt, songstress Rosemary Clooney, twice.
Danny Thomas was a Lebanese-American. He was a huge hit on early TV and his daughter Marlo was the Zoey Deschanel of sit-coms in the late 1960s.
Spain-born George Santayana was a famous Harvard professor in the late 19th and early 20th centuries. Wikipedia says his students at Harvard included "T. S. Eliot, Robert Frost, Gertrude Stein, Walter Lippmann, and W. E. B. Du Bois."
Marilyn Monroe was not married to Louis Armstrong.