Memos are not meant to express debatable personal arguments, memos are meant to express a company position. By widely spreading a personal view, the author impersonated the company in a way that the company does not endorse. As a culture manager, you just cannot let this kind of things happen.
Regarding the content of the "manifesto", the author should have known better. Even if it was genuinely true that women's biology explains the gender gap in technology, it is not provable - as in, there is simply no way to quantify the effect, if any. And using unprovable causes to justify a societal bias is not acceptable. The problem is that you can use unprovable statements to justify anything.
The debate regarding whether it is good or not to intervene at company level to try and change an industry culture is a perfectly healthy debate. Widely sharing one's view which uses unprovable arguments and that will offense some people is simply a dumb thing to do.