Besides Jon Udell’s examples of permissive whitelists destroying spontaneous association, here’s a another reason not to use such systems: they may be spamming the people who are emailing you. This sort of action does not appear to violate the privacy statement of that service.
Update: This was covered recently on Politech, and the response from Spam Arrest says that you’ll also get these spams if you were “added to one of our customer’s whitelist explicitly.” The Register has picked up on it…
