Reading it, it doesn't seem that what made an impression on you was PG's objective criticism of your idea that made your change your mind. It was that he was upset and said something mean. I think that because what you quote of what PG said and therefore must have made the most impact on your decision is his expressions that basically can be translated to "you are fucking stupid": "Moments like these make me glad we invested in sixty-four startups!", "If you want to drive off a cliff, go right ahead.", "like moths for bad ideas."
I suppose you want to be seen as rational actors and would never admit it, but when I read your post it seems like you reacted to PG's anger, frustration, meanness and other emotions, but not to his honesty. The conclusion I would draw from your anecdote is that it is much easier to get your point across if you are emotional, even when dealing with intelligent, technical people.