Do I believe this? Yes.
I have watched it with my own eyes.
I grew up in the very deep South in the 70s. Race mixing was frowned upon and often resulted in shunning from one's family. Very few people really wanted that. Oh, sure, there was a lot of mixed race dating, but just so teenagers could shock their parents. Absolutely no one was serious about race mixing.
Also, very few people I knew were all that interested in mixed marriages regarding religion or ethnic origins. Italians married Italians. Irish married Irish. Germans married Germans. You could get away with the ethnic thing, though, because of religious values though.
But by the late 70s and early 80s, all of this was dying. By the time I was 25, it wasn't so shocking to see blacks with whites and military men had long been bringing home Asian wives, especially the black ones.
As I look around now, race mixing is no longer a consideration for most people, other than just a preference. You know like "I like vanilla ice cream better than chocolate."
It seems like EVERYTIME I see little babies now, they are mixed race, and many of the mothers are unmarried. This was almost unheard of 30 years ago.
Nowadays, ethnic "pride" is seen as some sort of gang mentality or nationalism and is completely frowned upon unless it is related to Latinos or Blacks. You know---yea, your Cuban! Yea, your Nigerian! What's a Slovak?
It has happened really rapidly.
So yes, I believe it.
Do I believe that it is socially acceptable now? That's a hard one to grapple with, isn't it? But we were told for so long that considering our races and ethnicities was somehow hateful, so we decided to ignore it.