So why didn't you use the razor blade to cut Pidgin? I think you should make a separate section with big warning like "this software is not recommened because it privacy friendliness couldn't be proved. Found obvious privacy leaks:" and list software like Pidgin, Psi etc.
Also known solutions against obvious leaks should be listed too:
First, if user really needs exactly this protocol then you can't stop him. So let user to shoot himself in the foot avoiding stepping on known rakes.
Secondly, we don't know whether there are more privacy leaks in the software. May be listing known privacy leaks and solutions will be sufficient? At least we warn the user.