You could say the same about "ad hominem" or "straw man". I could just argue against anything by saying those things, even if they aren't true.

Let's look at motivated reasoning in this case. Google has diversity initiatives. What is their motive? Google exists to make money for their shareholders, the greatest beneficiaries being the executives and the board. Google has determined that they can be more successful (and therefore make more money) by being inclusive. Seriously now, how likely do you think it is that a company like Google is willing to give up their technical edge?

I had many engineering jobs when I was a junior programmer where there was a well defined interface, a well defined job for me to do, and I did it alone and submitted the code without review and it worked.

But, when I started working on teams and on more ambitious projects (some of my own invention), everything changed. Suddenly, I realized that I could achieve more by engineering people through writing design docs, code review, and cat-herding.

Yeha, it's less fun to program humans, but you can get more done.

There is a difference between proving something is possible and that something is True. Damore may have only demonstrated the first, but this is enough to refute the claim "There is sexism in tech because the gender ratio is not equal".

This is why it is important that group differences are in part responsible - it puts a burden on Google et al to find the magnitude if that influence, rather than attribute all of it to sexism. In other words, you can't attribute anything to sexism (without proof) as soon as there are multiple possible influences/causes.

It's basically impossible to discuss this subject without it being motivated reasoning. It's a profession in which it is notoriously difficult to measure aptitude and productivity. And it's a field of study that's a landmine for researchers to study for exactly the same reason as the fact that every single Damore-related thread here blows up into an uncivilized moderation war filled with name calling and insults.

We're still at a point where the science isn't pointing one way or the other and we haven't even settled on any decent metric to give to the scientists to calibrate any testing they'd be brave enough to explore. Is it any wonder that discussions on this topic are rife with confirmation bias? We're not going to approach anything resembling a productive conversation on this topic until both sides concede that the other side might have some point and that the true answer, as almost all true answers do, lies somewhere in between the polar ends of the spectrum that people argue from.

Slightly off-topic, most "logical fallacies" actually have very important heuristic uses. Just to get the ball rolling, "ad hominem" becomes extremely useful in a world in which we have limited access to full information, and have to constantly evaluate the reliability of outside parties.