While this will undoubtedly shrink some email lists, most of those people weren't going to be interested and buy (or whatever the action is) anyway. If you're doing email marketing, you should expect that a certain percentage of people will unsubscribe from any given email not because it's a bad email but they are just no longer interested. Making it more difficult for someone to unsubscribe just increases the likelihood that they'll complain or report it as spam and no one really benefits from that.