I disagree with you that it should be per poster rather than per journal/community. Indexing/searching controls are almost always handled on a per journal/community basis (the only time I can think of that's different is for following specific comment threads), and I don't see a great justification for changing that in this specific instance. If drama breaks out in the comments, the journal owner/community mod is the person who will have the tools/authority to deal with it, so I think they should be given control over possibly drama causing settings.