In my opinion, no-one else than the author should be allowed to port his/her mods. Most of the people who port without permission won`t even bother to test their ported mod, which fills the Add-Ons and Maps section with Failbin material. TDM is a good example of this, it has been tried to be ported multiple times.
And what about the mods that deserve to stay unported? Most of the authors know if they should port their creation or not. Badspot should add a rule about this.