Prior to the mid 20th century, there were relatively few multiracial families compared to today. Many people would hide their multiracial heritage due to segregation laws, marriage laws, and taboos against racial mixing.
I believe the turning point was WWII when millions of American were exposed to other cultures and races, the growth of world trade, and world tourism. The isolationism, racism, and xenophobia of the first half of the 20th century in America began slipping away. By the 21st century interracial and cross culture marriages had become so common, that few people even noticed.
I think by the mid 21st century, racial discussions such as these will become very rare because the attitudes toward race and ethnicity is changing so fast among the young people. It's not that they don't notice race and ethnicity; it's just not that important to them.
Race and ethnicity which once was considered the defining characteristics of ones personality, character, and intelligence is fast becoming just another demographics.
However, no matter how few racist and xenophobes there may be, I'm sure they will find a home at USMB.