It's not a special immunity, it's a special vulnerability which some people have. For most people reading the forbidden topic would be safe. Unfortunately most of those people don't take the matter serious enough so allowing them to read it is not safe for others.
EDIT: Removed first paragraph since it might have served as a minor clue.
Interesting.
Well, if that's the case, I can state with high confidence that I am not vulnerable to the forbidden idea. I don't believe it, and even if I saw something that would rationally convince me, I am too much of a constitutional optimist to let that kind of danger get me.
So, what's the secret knock so people will tell me the secret? I promise I can keep a secret, and I know I can keep a promise. In fact, the past shows that I am more likely to draw attention to the idea accidentally, in ignorance, than deliberately.
(Of course, I would have to know a little more about the extent of my promise before I'd consider it binding. But I believe I'd make such a promise, once I knew more about its bounds.)
Some research says that lurkers make up over 90% of online groups. I suspect that Less Wrong has an even higher percentage of lurkers than other online communities.
Please post a comment in this thread saying "Hi." You can say more if you want, but just posting "Hi" is good for a guaranteed free point of karma.
Also see the introduction thread.