One possible way Google could have turned this into a win-win scenario would have been to have the VP of diversity co-opt the memos's authors and put them in charge of some diversity initiatives so that they could experience the nuances of the problems with their viewpoint and perhaps the come to a revised (and usable solution), or if his berries were more closely correct the VP could experience that.
It's an inherently unfair game. It doesn't matter how many crisis did she prevent, she didn't prevent one and that should not be enough to fire her.
Having said that, I assume this was not the first time he expressed his opinions about diversity hiring. The company should keep an eye on this kind of sentiment and use the information to guide its own behavior. If I knew diversity hires were creating such perceptions, I'd boost internal campaigns to better inform the workforce of the methods and intended results, as well as publish indicators that allow a fair assessment of its results.
I don't think, for a second, the bar was lowered. It's just that there is more than one bar.