Because the decision to initiate a particular kind of public discussion entails everyone else in the organization taking on a certain level of risk, and an organization should be able to determine what kinds of communal risk it's willing to allow its individual members to force on everyone else. There are jurisdictions where criminal incitement is itself a crime.
I can't say whether I agree or disagree until you precise the meaning of the qualifiers "particular" and "certain". But my question was in any case probably directed a bit elsewhere: if the members shouldn't be free to write about certain class of topics because they may misjudge how the society at large would react, doesn't it imply that they shouldn't be free to write about anything because they may misjudge what the society at large might think? If the rationale is that which you say, returning back from abolitionists to LW, shouldn't the policy be "any post that is in conflict with LW interest can be deleted" rather than the overly specific rule concerning violence and only violence?
New proposed censorship policy:
Any post or comment which advocates or 'asks about' violence against sufficiently identifiable real people or groups (as opposed to aliens or hypothetical people on trolley tracks) may be deleted, along with replies that also contain the info necessary to visualize violence against real people.
Reason: Talking about such violence makes that violence more probable, and makes LW look bad; and numerous message boards across the Earth censor discussion of various subtypes of proposed criminal activity without anything bad happening to them.
More generally: Posts or comments advocating or 'asking about' violation of laws that are actually enforced against middle-class people (e.g., kidnapping, not anti-marijuana laws) may at the admins' option be censored on the grounds that it makes LW look bad and that anyone talking about a proposed crime on the Internet fails forever as a criminal (i.e., even if a proposed conspiratorial crime were in fact good, there would still be net negative expected utility from talking about it on the Internet; if it's a bad idea, promoting it conceptually by discussing it is also a bad idea; therefore and in full generality this is a low-value form of discussion).
This is not a poll, but I am asking in advance if anyone has non-obvious consequences they want to point out or policy considerations they would like to raise. In other words, the form of this discussion is not 'Do you like this?' - you probably have a different cost function from people who are held responsible for how LW looks as a whole - but rather, 'Are there any predictable consequences we didn't think of that you would like to point out, and possibly bet on with us if there's a good way to settle the bet?'
Yes, a post of this type was just recently made. I will not link to it, since this censorship policy implies that it will shortly be deleted, and reproducing the info necessary to say who was hypothetically targeted and why would be against the policy.