Alternatively, the people dismissing the idea out of hand are not taking it seriously and thus not triggering the information hazard.

Also the censorship of the basilisk was by no means the most troubling part of the Roko incident, and as long as people focus on that they're not focusing on the more disturbing issues.

Edit: The most troubling part were some comments, also deleted, indicating just how fanatically loyal some of Eliezer's followers are.