Sorry for your frustration. I understand the idea behind forums having a minimum # of posts required prior to using the "for sale / rent" sections, but you have over 200 posts. I'm not sure what the mimimum number of required posts to use the "Rent" section is, but I can't imagine why it would be above and beyond 200! In most online communities, you would be considered an "established" user. Many other non-Disney forums that I participate on require somewhere between 10 and 50 posts, which I think is much more reasonable. The posting restriction is in place to prevent new members from spamming the for sale sections, and obviously, you're not trying to do that. Perhaps you can shoot a PM to the Rent/Trade forum admin to see if they can waive the fee for you, seeing as how you are a 10 year memember, and this is your first attempt at trying to rent out points. I don't feel that to be an unreasonable request, and would at least try that before pulling the pin on DIS.
In the event that you don't receive satisfaction, you absolutely have the right to use the broker of your choice (how wonderful that we live in a free country.... for now). Even though I am not buying from TTSS, I received good service from them in my recent resale search. But they're not the only game in town, and the other three major brokers that I dealt with provided excellent service as well. As a seller, I think you get a little more exposure from the TTSS, simply because they are the largest. But the fact that they don't co-broker, while the other major ones do, probably makes up for that.
We'd hate to see you leave DIS, and unfortunately, the only person that you would really be hurting is yourself, as there isn't another resource on the net that compares (IMHO). But I can't argue with your logic, and if that's what you choose, I can't say that I blame you.