We can all understand the desire and need for dealers and other such groups to have private forums. If you go to a knife show, there's often a private back room for the dealers.
But, what about everyone else. Should there be private forums just because one group doesn't want "certain people" cutting in (obligatory knife reference there, "cutting in")?
Have you ever been at a party where everything is just going great, everyone's having a good time, everyone is nice, you're having a great time, and then some obnoxious person shows up and, one by one, everyone suddenly has a headache or remembers they're double parked, or has to get up early tomorrow, or has a sick child at home they have to get home to, and the whole thing just sort of collapses? One bad person can spoil the mode for everyone.
I participate on a lot of on-line discussions, this forum, other knife related groups, and other groups related to other interests. The best ones are the private list servers where you have to be invited. Everyone is polite, everyone contributes, everyone stays mostly on-topic, and a sort of community forms. We disagree sometimes, sure, but everything stays productive.
I can see why some groups within the knife collecting community might want to give this a try.