I don't know if it's possible to set up a mailing list or a separate forum for invitees only, but I'm also not sure whether it would be worth the trouble. The 'abuse' was hurled by just a few people, and most of I wouldn't even call abuse. Ever since Qinghua Ding engaged here, the 'abuse' has become even less. On the other hand he does say (based on his research) that the Arctic won't go ice-free for another 50-100 years, so some push-back is to be expected on a forum for people who are worried about AGW.