That's just like, your opinion man.
Everyone agrees it was polite, but well-argued and coherent is where not everyone does agree.
I've seen people with advanced degrees host debates where they legitimately advocated creationism as the truth against evolutionary biologists with equally advanced degrees. They were polite, and their supporters would say well-argued and coherent. But anyone who knows anything about the topic would see that the creationists weren't actually adding to the discussion or making strong points at all. Those creationist debates are always unsatisfying and exhausting to listen to, and after a while, that schtick becomes old and non-creationists stop engaging because it's just boring. But creationists will attend and be excited every time because having a debate against a real scientist legitimizes them.
That's how this memo thing felt. Nothing new was added to the discussion (at least not to those of us who have had this discussion before) and it just seemed like an opportunity that some less savory folks jumped on to promote some out-dated views (and more importantly, for mainstream media to jump on to paint all of tech as a place where those views are the norm. That story sells despite how wrong it is).
FWIW, I do hate impoliteness though. I understand why people felt defensive for the author after watching the internet freak the hell out (in rude or dismissive ways) about the memo which was not impolite in itself.