When you're an expert, being an expert becomes part of your personal identity. If someone challenges your work, you take that as a personal affront, as if they're challenging you. And if you're an expert that's towards the front of a giant mob, and the giant mob is listening to you, then that other guy's not just challenging you, he's challenging your position within the mob. All those hardwired primate signal paths light up in your brain and influence your behavior to avoid losing your position within that mob.