The fact that you immediately equated "diversity" to "lowering your hiring bar" and "under-performing" is as ignorant as it is insulting.
Women and brown people are not lower quality humans, and it has been shown over and over and over that companies who hire for diversity perform better.
I think ignorance is taking things out of context unnecessarily. I am assuming Pinterest already has an unbiased hiring bar. Yet, due to sheer probability, the number of other races get hired much more. Considering the number of applicants remain the same, how do you balance the race/gender without being biased to one race/cast?
Women and brown people are not lower quality humans, and it has been shown over and over and over that companies who hire for diversity perform better.
http://lmgtfy.com/?q=do+diverse+companies+perform+better