Taking this post in the way it was intended i.e. 'are there any reasons why such a policy would make people more likely to attribute violent intent to LW' I can think of one:

The fact that this policy is seen as necessary could imply that LW has a particular problem with members advocating violence. Basically, I could envision the one as saying: 'LW members advocate violence so often that they had to institute a specific policy just to avoid looking bad to the outside world'

And, of course, statements like 'if a proposed conspiratorial crime were in fact good you shouldn't talk about it on the internet' make for good out-of-context excerpts.