You see, everyone chooses a strategy around their teens or even into their twenties to say why they are valuable, why they have a right to exist. A woman might choose: sexy, smart, beautiful, motherly, etc. And that becomes their identity. So attacking that (call a smart person "stupid" and they'll light up) is attacking their entire identity, what they've chosen as their right to exist. Have you seen a university professor in a tweed jacket? There you go.
The framesets I mentioned are tied to that identity and defended with that same "raison d'etre" fierceness. Information that violates the frameset, violates the identity strategy. It's like you have all your money in a particular stock and someone is saying something negative about the company. The more stake you have in that company, and the more fear you have of it crashing, the more unwilling you will be to be rational about what others may say.
Following the analogy, it might seem that diversifying is the answer: you're smart, but also into extreme sports and healthy, etc. That's not really the answer, though. The trick is to get your money out of the stock market; you have to care as little as possible what people think. Sound easy? It's one of the hardest things you can possibly do.