I am familiar with the SpamHaus PBL. It was my understanding that anyone could easily remove their own IP address from the list if required? Presumably that is

I am familiar with the SpamHaus PBL. It was my understanding that anyone could easily remove their own IP address from the list if required? Presumably that is what happens when Rackspace customers want to send legitimate mail. So why would it cause any problems for spammers?