Earlier quoted context omitted.
I'm experimenting with it and I might get rid of it. It's mostly just to try to keep the group active, because it's a small group and if the activity level dies out, the group dies out. But thanks for the feedback, I'm making a note of it.
I once watched a livejournal group die in my general takeaway from that was that people might get annoyed when you tell them what they are not allowed to do on your site, but most of them will roll their eyes and put up with it. if you tell them what they have to do they will simply drop the site and never look back.
I do my best to make the activity requirements clear upfront, so the only people who will be upset are those who choose not to sign up anyway. For me, the far bigger challenge is learning how to define these "rules" in a way that makes the group sustainable over the long run - which is to the benefit of everyone involved. While the idea of having to post once every 25 days may seem unnecessary, if 100 people followed it to a tee, you're going to have a group that remains active indefinitely.
I do see your point, and I agree that if any sorts of hard rules are to be imposed upon a discussion, it needs to be done tactfully.