There’s something to be said for exclusivity.
Whether it’s offline (speciality professional groups, support groups, and local chambers of commerce), or online, you’re going to get more accomplished if there is a base level of commonality.
Exclusivity gives groups direction. You’re less likely to spend time trying to decide what actions to take, or topics to discuss, if everyone is there for a specific reason, or has some common thread.
While a by-product of that can sometimes be groupthink, the benefits often outweigh the downsides. Online it’s much the same. Building an online community that has specific requirements to entry, and those requirements are strictly enforced, the overall quality of the interaction goes up.
It is well worth understanding and articulating the barriers to participation of your community and making sure they are aligned with your goals. Barriers to participation exist in every community and while it is often good to make those as low as possible the same can be said for the reverse. Barriers to entry qualify members and often the highest barriers create the most affinity.
The barriers to entry that you put up in an online community must be for a greater good. They must serve the larger goal of the community, whatever that might be.
Communicating the level of exclusivity to members that already exist also ensures that they will be vetting any colleagues or friends before suggesting the join the community, knowing full well what the requirements are to join.
When the goal is quality not quantity, some level of exclusivity, as well as an apparatus to enforce those standards, must exist to ensure that the community remains on track.