Now this is a tough one esp since you talking about proofs. Can you provide links to all those 6000+ posts here ?
Ok, Now coming back to the Issue we have in hand.
1: What is wrong in Profs going through the forum ? Atleast ppl wont address the profs as "Kalu mota" or "Yamraj" anymore.
2: Making a mandatory members only forum, will drive out a few ppl from here. Havent seen any forum being successful, by making it members only. (Dont give Warez/p0rn examples here

)
3: In the future, we might come up with a "members only" section. Entry criteria is still open for debate.

4: But yeah, I know a few ppl rip the GD/PI exp posted here, and post it on their own sites/groups. Now this can be a serious concern.