You just don't get it.
You're part of an admin team of an internet forum, you get a new member who happens to mention they are an ex member of the religion that you belong to and straight away you're in a spin about whether to ban them or not. You know nothing about this person, you haven't even given them a chance to show you anything about themselves... but you're considering banning them. 
The fact that you're worried about the numbers on your board... are you saying that if you had plenty of posters you wouldn't hesitate in banning that person?
You're displaying an attitude that says to me you should not be an admin in the first place. It's the internet... you're going to get people registering with opinions and beliefs that are different to yours. If you're so opposed to ex-jw's registering on your site, you should be mentioning that in the sign up agreement in the first place.
This btw... is coming from someone who admins her own forum.