I agree withbiondoa . I think bettas should always be kept on their own.
Betta "communities" are usually a short term experience. The betta either is too stressed from all of the fish in there and doesn't live out it's lifespan.....
Is this your personal experience with them?
I've had groups of female bettas live several years in community settings. The only issue I have with them in this type of setting is their tendency to over-eat.