Everything you mentioned is inextricably intertwined with the reasons in my comment.
We're talking about the same folks; marks who subconsciously wanted to be duped.
They are 'frustrated' because that American Fallacy I mentioned? That long con was only directed at White people; everyone else inherently knew that they were never even considered a part of the equation.
They are 'scared' because all many of them have ever had was the 'cold comfort' of not being Black (or Brown, or Gay... etc.) Take away that unofficial privilege, that automatic assumption of being the 'normative' archetype, and what do such people have left?
To quote a line from Mississippi Burning;
"If you ain't better than a nigger, than who ARE you better than?"
Lastly, the aforementioned 'relentless insistence' is a symptom of entrenched cognitive dissonance which stems from decades of psychological manipulation by big business... people who are complacent, insecure and poorly educated are easy to control and manipulate...