The point is if there aren't enough QUALIFIED C and you want to just bring in as many Cs as you can find, even to the extent of relaxing the qualification requirements that A and B are subject to, that is discriminatory. It should be pretty logical that if there aren't enough women WANTING to go into STEM, not as many will be going to school and training in it, and thus it's harder to find as many qualified ones to join google. Remember that intelligence and talent are only part of the job. You also have to have education and training in the field you are entering.
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That's exactly my point. There is certainly more diversity in representation today than when Google was founded, but even you admit that you cannot find evidence to show whether the company is better for it.
And just as Damore could not defend his argument without demonstrating that Google has gotten worse with higher diversity, you also lack the evidence to prove that increased diversity has been beneficial. Based on this, why would you not even consider reexamining the practice of diversity hiring and its true consequences? And why are you so adamant in supporting it?
The answer of course is: it's all just political. Google doesn't want to go against mainstream society any more than most individual Google employees are willing to go against Google. Social engineering.