The point is that progressives should stop being so afraid of accepting genetic differences, because they don't go against the type of policies most progressive

The point is that progressives should stop being so afraid of accepting genetic differences, because they don't go against the type of policies most progressives are after. And because genetic differences are probably real, when progressives argue against racism etc. because "genetic differences don't exist" they actually hurt their position. Policies that discriminate based on genetics are bad, not because genetic differences aren't real, but because they're a) inaccurate, especially compared to measuring the differences themselves, and b) usually immoral, because having good genetics is luck and doesn't make you deserve a better life. Chomsky (see above comment) probably does a better job explaining this.