Another reason why the existence of IQ as a largely inherited feature is unacceptable is the simple fact that half (50%) of the population is below average, condemned to live out their lives in a inferior social position. If IQ is so important and it is immutable, then there are no real ways for social advancement. Maybe beauty, but little else. And if it is inherited, then the Dream of the Jewish Mother (“My Son, The Doctor!”) is unreal. Hopelessness would be a sure receipt for social restlessness, at least in a democracy.
Not that the recognition of IQ would make society unworkable. Many (maybe most) societies were organized in a pyramidal way, with a King supposedly divine, descended from the Sun (like the Japanese Emperor), and an hereditary caste of aristocrats or samurais. One is born into these castes, no merit could make one a divine king or a noble samurai. People accepted this state of affairs as normal and went on with their lives. But we in the West cannot go back and restate a hierarchical society. Too many people has a stake in the current system.
And the French Republic (Napoleon!) has shown the superior fighting power of democracies over autocracies. There is no way to go back. Egalite has triumphed.
I have to disagree with that last. We will go back. The difference is, how much of civilization will we lose before the egalitarian experiment collapses, leaving us to rebuild on its rubble. While fighting off the savages egalitarianism has unleashed.