Sure, I understand. But it's not just about people signing up and using AppleTalk for trades rather than discussion, it's also the possibility of scammers.
If we don't have access restrictions on the trading forum, we expose our users to getting scammed more easily than if the trading forum was only open to established members of the community. Of course, that's not saying established members won't scam other members, but it's about lowering risk.
I don't know about you, but I'd rather carry the burden of less trades than having to suffer the repercussions of one of our members getting scammed. Obviously if someone does get scammed it won't all be on me, but I'd feel responsible — especially if it was because the trading forums had no access restrictions.
So yeah, trading forum restrictions are here to stay.