I personally find the problem of 'spam' or 'trolling' to be a small part of 'off-topic' posting. HN and digg don't have categories, right? So the on-topic mater

I personally find the problem of 'spam' or 'trolling' to be a small part of 'off-topic' posting. HN and digg don't have categories, right? So the on-topic material is quite broad. (Even better, personally, is permitting categorization such as sub-reddits, but with inheritance.) Still, the complaint is basically that one person thought article A was on-topic (hey it's my new blog! hey buy viagra!) and another person thought it was not. An alternative to restricting the user-base--which I think will just reduce the variety of submission perspectives and depth, and only prevent off-topic-ness so much as the community is homogenous--is to A. Make the "topic-ness" very clear. This might include reminder text or tutorials or mission statements, and it include the comments and voting mechanisms we already employ to pass-on the culture. B. Use natural language processing and automation (at least for flagging) to reduce off-topic submissions.