When you say "I'm passionate about [something]." What you really mean is: "Any viewpoint that is not in lockstep with my own is abhorrent, and will be treated as such. Also, I am immune to any line of reasoning which does not lead to my exact position on this issue, and I am allergic to any fact that could potentially paint my position in a negative light. Lastly, there is no such thing as a 'logical fallacy,' so long as it supports my position."

When you say "I'm passionate about [something]," that becomes the one thing that I absolutely will not talk to you about.