I remain unconvinced. Yes, the arguments presented here are persuasive, but we're talking social phenomena here - nothing is black and white, there are no unbreakable rules.

So use the analysis to design a system that works in spite of these pressures. Perhaps you can start by being less restrictive of the membership and the topics, and then become more restrictive once you've gained users. Perhaps those who are contributing directly to the core subject can be rewarded in some way, and see an impact in the "real world," such as more exposure in relevant communities, more followers for their blog or on twitter, or similar.

Break the rules. At least, break the rules that need to be broken.

This piece finds rules that need to be broken. Find a way.