It really depends on the forum.
There are a lot of Disney forums and resources out there. The legitimate Disney information and trip planning sites are all open to anyone, and a lot of them offer great information.
The boards that are "closed", requiring a membership or an invitation to join, are generally social gossip type sites. Most of them are not really Disney sites at all, although some of them do make sport of reading posts on the other sites and then ridiculing or disrupting their targets.
It's really up to each individual to determine what kind of experience and community they are looking for. It takes all kinds, right?
The one thing I will add is that anyone who's an actively participating member of a community that is hostile toward the DISboards or engages in harassing or ridiculing our posters won't be welcome to participate here, as you would expect.