I put together a quick table
Should you charge people to be a member of your online community?
Charging for membership might be a very good idea.
It forces you to provide a level of service that reflects the price you charge. It also narrows your focus to fewer people (also good) and gives you a direct revenue. Direct revenue means either profit for your business (if you're hired to do this) or the chance of a full time job (if you build communities solo).