You make good points.
However, facts are what they are, and pretending they are something that they are not, or refusing to examine them to determine their truth or falsity, will not help anybody.
Let’s look at it another way. If you are constantly told there is no actual difference between your race and another, yet your race consistently does less well, what is the only remaining explanation?
Well, it must be that the other race is keeping your’s down, intentionally or not. A recipe, if there ever was one, for brewing resentment, hatred and a desire for revenge. And, of course, if there actually are differences, it is a situation that simply cannot be ameliorated.
I would love it if the Declaration of Independence were literally, rather than metaphorically, true. That all men, and all groups of men, are literally equal in every way.
But my desire for that does not change the facts as they exist. And a considered refusal to find out what those facts are also will not change them.
It seems to me that it would provide a defining rationale for segregation and apartheid, and a rationale against the viability of equality. Self-discrimination and segregation would accelerate, and the resultant anger and civil unrest would just create a vicious circle towards ethnic violence.
Resentment would be much greater than it would if they only believed racism from an established minority was the problem, than if they were to compelled to believe that their own racial weaknesses were the problem. Not to mention that they would likely reject conclusive results as racist propaganda, as an unprecedented display of racial oppression.