That is literally the whole point of his memo, that women have a different (i.e, worse, in this context) statistical distribution of ability and inclination to the tech field.

> “How dare he question the effectiveness of affirmative action” is also not an argument.

Sure it is. His argument is structured as follows:

1. Negative effect Q is caused by both A and B. 2. We can't do anything about A. 3. Therefore we shouldn't do anything about B.

That's just bad reasoning.