I would be inclined to go with the opinion of those that moderate, or have moderated in the past, when it comes to deciding whether to open the forum to all.
For a regular, bog standard member, like myself, it's very easy to ignore the naughty posts . It's obviously not so easy if you have to try and moderate.
Surely we all know the best way to deal with antagonistic posters, who just about manage to stay on the right side of the rules.....ignore them!