Firstly, if there's an unspeakable danger, surely it'd be best to try and not let others be exposed, so this one's really a question of if it's dangerous
Not quite. It's a question of what the probability that it's dangerous is, what the magnitude of the effect is if so, what the cost (including goodwill and credibility) to suppressing it are, and what the cost (including psychological harm to third parties) to not suppressing it is. To make a proper judgement, you must determine all four of these, separately, and perform the expected utility computation (probabiltiy effect-if-dangerous + effect-if-not-dangerous vs cost). A sufficiently large magnitude of effect is sufficient to outweigh both* a small probability and large cost.
That's the problem here. Some people see a small probability, round it off to 0, and see that the effect-if-not-dangerous isn't huge, and conclude that it's ok to talk about it, without computing the expected utility.
I tell you that I have done the computation, and that the utility of hearing, discussing, and allowing discussion of the banned topic are all negative. Furthermore, they are negative by enough orders of magnitude that I believe anyone who concludes otherwise must be either missing a piece of information vital to the computation, or have made an error in their reasoning. They remain negative even if one of the probability or the effect-if-not-dangerous is set to zero. Both missing information and miscalculation are especially likely - the former because information is not readily shared on this topic, and the latter because it is inherently confusing.
Tiny probabilities of vast utilities again?
Some of us are okay with rejecting Pascal's Mugging by using heuristics and injunctions, even though the expected utility calculation contradicts our choice. Why not reject the basilisk in the same way?
For what it's worth, over the last few weeks I've slowly updated to considering the ban a Very Bad Thing. One of the reasons: the CEV document hasn't changed (or even been marked dubious/obsolete), though it really should have.
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.