Re: How to define topics for forums?
BuddyPress -> Component Setup–>Let users create, join and participate in groups would seem to be for disabling Groups entirely, so that’s not it.
Not sure what I had in mind, there. I wonder if you can hook Buddypress permissions into Justin Tadlock’s excellent Members plugin (http://justintadlock.com/archives/2009/09/17/members-wordpress-plugin)
Basically I’d just disallow Subscribers (if that’s your default role) from creating groups, but I’d have to go digging to figure out how to do that….
I haven’t actually tried!