I'm aware that the concepts of "white" and "black" are concoctions. However the reality of our world is here to stay. And the concept of race will always be with us. I measure it through the common experiences shared by my people. And the black man as the world has defined him is considered to be lowest of all and treat accordingly. Whites only use biracial people to confuse blacks about who they are. Due to the presence of white supremacy, hierarchies are created on the basis of skin complexion and features within groups. If biracial people weren't considered black by us this wouldn't even be an issue.
What history should they take pride in?
What culture should they adopt?
How do we define a biracial who is Asian/Black versus one who is White/Arab? How do we differentiate the different admixture percentages : octoroon, quadroon? How many different terms for all the different possible mixtures do we come up with?
Do we put everyone through a genealogy test and get their percentages before we allow people to call themselves Black?
At what percentage do you go from Black or White to multigenerational mixed?
It's funny because including all biracials as Black, which isn't the reality (Tiger Woods doesn't consider himself Black) AND what you are proposing, no biracial be considered Black is essentially the same thing, especially considering that people in the same bloodline has different admixtures and percentages and thus the tedious classifications would be something only a person would inferiority complex would entertain in the first place.