I have little doubt that some smart people honestly believe that it's dangerous. The deletions are sufficient evidence of that belief for me. The belief, however, is not sufficient evidence for me of the actual danger, given that I see such danger as implausible on the face of it. In other words, sure, it gets deleted in the world where it's dangerous, as in the world where people falsely believe it is. Any good Bayesian should consider both possibilities. I happen to think that the latter is more probable. However, of course I grant that there is some possibility that I'm wrong, so I assign some weight to this alleged danger. The important point is that that is not enough, because the value of free expression and debate weighs on the other side. Even if I grant "full" weight to the alleged danger, I'm not sure it beats free expression. There are a lot of dangerous ideas - for example, dispensationalist christianity - and, while I'd probably be willing to suppress them if I had the power to do so cleanly, I think any real-world efforts of mine to do so would be a net negative because I'd harm free debate and lower my own credibility while failing to supress the idea. Since the forbidden idea, insofar as I know what it is, seems far more likely to independently occur to various people than something like dispensationalism, while the idea of suppressing it is less likely to do so than in that case, I think that such an argument is even stronger in this case.