Here is the connection between member payment and specific group - from Mark's original message in this thread:
"Once the free member slots are filled up, someone wishing to be a new member of the group would have to pay a yearly fee to Groups.io."
This creates a direct connection between a specific group, on the one hand, and a member having, or wanting, to get a paid membership, on the other. And this is what I mean by the space warping around groups. People would not be just signing up for a yearly paid membership in groups.io, no matter what groups they want to join, and no matter whether or not those groups are "full." People would try to join a group, discover that it's at its limit, and THEN have to pay groups.io in order to join it. In all respects except technically, that's the same as someone paying to join a specific group.
Messages are the sole opinion of the author, especially the fishy ones.