Can a plugin be made where members have to login to view the forum. If not a box will have to appear saying "You must login to access this forum." And also saying "Please login below, or register for an account."
You can already set forums to "Private" for "logged in" Members only to view, or you could set passwords for forums. Other than that IMO I'd be pretty annoyed if as a Member I'd have to log in every time I wanted to see a forum.