"White supremacy" as a movement, as a phrase in common usage, and as a matter of common sense, implies a whole host of beliefs and policy desires that aren't held or sought by Charles Murray or his defenders.

Not holding those beliefs doesn't render you a "benevolent supremacist;" it means, very plainly (and using ordinary definitions of ordinary words) that you're not a supremecist.

It is plainly misleading and obfuscatory to apply that term to anyone investigating population differences in good faith.

Perhaps you mean to say that all such investigations are evidence of nefarious motives? I think that's wrong, but it's at least a coherent worldview.