Uhh I don't think he was defensive at all. I think he made a very good point.
I would bet large amounts of bitcoins that no VC wrote any of this, save MAYBE part of the opening. It's extremely verbose and the business analysis ultimately is a smaller part of what amounts to just a rant about the quora community.
And if you want to read that, that's great. I don't. I've read the exact same criticism of Wikipedia, Reddit, <insert social community here>. It doesn't really provide any insight I didn't know already: big social communities tend to get co-opted by people with agendas and too much time on their hand. Cool.
Talking about company strategy and why it is unlikely to be successful is interesting, and provides good salient points for the rest of us. Talking about 'rad fems' taking over Quora? Not so much.