I'm going to spell out my concern more elaborately, Just to make sure if I understand your suggestion correctly.
If I have 3 user groups: Red, Green and Blue. Each of these groups has a private section in the forum. If I use the correct tags, only users of the respective groups should be able to see their private area, right? Or atleast, that's what I'm trying to achieve.
A guest user who has not logged in, should not be able to see the private sections listed on the side. Same goes for other users who are not in the Red, Green, Blue groups. Only after logging in do Red users see the Red private section and so on.