It's a first principal in liberal ideology that all races and genders are equally attractive , intelligent, and are equal in any other positive attribute imaginable and only differ in skin color and gender identity. Further, all people are roughly equal in all characteristics and the only thing that differentiates them is upbringing, access to opportunity and systemic discrimination toward or against them.

No amount of empirical data matters because it is a first principal which the whole rest of the political ideology relies upon. If someone does not accept this as a first principal and is willing to examine empirical data that contradicts it and draw the conclusion that all people are not equal, then they are no longer a liberal.