can you conceive of a reason (not necessarily the officially stated one) that the actual basilisk discussion ought to be suppressed, even at the cost of the damage done to LW credibility (such as it is) by an offsite discussion of such suppression?

The basilisk is harmless. Eliezer knows this. The streisand effect was the intended consequence of the censor. The hope is that people who become aware of the basilisk will increase their priors for the existence of real information hazards, and will in the future be less likely to read anything marked as such. It's all a clever memetic inoculation program!

disclaimer : I don't actually believe this.