It seems to me that when people make a post in a group and choose the option for it to appear on the main mesage boards, that people should be able to respond.comment form the main board without having to join the group it was posted in.
I see quite a few interesting posts, but I don't want want to have join every group, they come out of just to respond or comment.
That depends if the group in question requires you to join first or not. Not all groups make you join first in order to comment. I know what you mean about the groups, I host three on here and just don't have the time to dedicate to being in more groups.