First you say this:
>> for that sexism play A role, not the ONLY role in creating the gender discrepancy
Then you say this:
>> Yet of all the women I've known most weren't driven to excel to the same level of most men I've known.
I'll give you the benefit of the doubt in that I'm going to assume that it wasn't your intention to make a disturbingly sexist remark in a discussion about sexism.
You can replace women with African-American, and what you wrote sounds an awful lot like the racist drivel that came out of the South for 200 years. If anything, the author of the memo's attempts to argue that there is some biological basis for discrimination only serve to weaken his position. Furthermore, this 'biological differences basis' for discrimination eventually leads us to eugenics if taken to its illogical extreme. And yes, people have taken it that far in the not so recent past.
In the cases where what you wrote is even partially true, that some women (appear on the surface) to be less ambitious and less driven than men, did you ever stop to ask yourself why?
I've worked in tech my entire career, and I've witnessed appalling sexism. I have watched with my own eyes while women suffered humiliations like being told things like "no one invites you to meetings because you can't keep anything secret". Then there are things like code reviews. At work we recently had to institute a 'no abusive code review' policy because a small cadre of the men were using the code review process to hammer several of the few female engineers we've managed to somehow convince to come work for us. Like most places, our workplace policies are required largely due to behavior that was originated by men.
It seems like it's awfully easy to forget that women are half our species! How can anyone in their right mind think that sexism, unconscious or otherwise, is okay? How can anyone think that it's because 'women are less driven to succeed'? How can anyone think this when half their DNA comes from a man and the other half from a woman?
As a gay man (a gender/sexual minority), I can actually relate to how awful it feels to be treated like a second class citizen simply because of something that I do not feel like I can change (my sexual orientation). I'm not sure how much money it has cost me, but at the very least it has cost me the difference in filing single vs. filing jointly for the first 17 years of my marriage. Women pay similar costs when they're paid less over the course of their career, and/or when they're denied promotions for 'being ambitious'.
The attitude that underlies your comment -that you could actually believe that what you wrote is true and somehow justifies unequal treatment- is utterly, totally, and exactly why we need the programs the author of the now infamous memo argues against.