if anyone is making the group less Fun or scaring off new members, and yes this includes being a creep who offends potential heroine recruits, give them an instant ultimatum or just fire them on the spot.

Consider who might resent a friend's exclusion from the group, especially if it appears capricious. If there are clear norms and people are emotionally prepared to accept the group's priorities (who it wants to include/exclude), then the collateral damage of a person's friends leaving in protest would be taken with relative equanimity by those who remain.