No, it isn't. Not when many of their female employees were willing to leave the company, and when the existence of that manifesto would make their recruiting efforts much, much harder.
Google had to decide which they value more: Damore's memo, or their legal defense against inevitable discrimination suits.
---
nb. Large companies are a constant target for litigants of all stripes. There are suits of all types filed against them regularly. They must be careful or, under current law, a bitter employee who was not in actuality discriminated against can successfully claim discrimination and pilfer millions of dollars from the company, inviting follow-on after follow-on. Because the current law is based upon reading in/assuming specific motives to otherwise-valid actions, companies are forced to assume a defensive legal position, such that the other side's lawyer will have a large amount of difficulty convincing a judge and/or jury that such motives were allowed or tolerated.
Google had to decide which they value more: Demore's manifesto, or the contributions of a third of their workforce.