This seems to be another version of: "the pipeline of potential talent from colleges has very few women, so if we go out of our way to hire extra women, we'll reduce our overall hiring quality. The college pipeline needs to be fixed first."
Even if you concede that, here's something I don't see discussed often: hiring more women and minorities in big tech companies now could help to fix the college pipeline in future. If tech companies are seen to be diverse, welcoming environments, maybe more kids of all backgrounds will get interested in tech in the first place.
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