Cleaning up a block of IPs previously used by shady characters has a real cost, both in time and money. The argument as I see it is who bears the responsibility and cost of that cleanup.
... and as we all know the fundamental axiom of Internet economics is to foist of as many of your costs as possible on someone else. If you get a new chunk of IP space, you find that it's listed in a lot of private blacklists, and you're not able to get them to unlist you, the reasonable conclusion is that they DO NOT CARE that you can't send them mail. A way to get them to care is to get their own customers, i.e., the people to whom you are trying to send the mail, to complain to their mail managers. If that doesn't work, it either means that the managers are incompetent, or that the recipients also DO NOT CARE that you can't send them mail. I would guess that the latter situation occurs a lot more than the former. Telling people to time out their listings automatically is a non-starter, because they will find nearly all of them are still spamming or sending no mail at all, and an infinitesimal trickle switched to sending legit mail. Who's going to do that? Spam sucks, largely because spam is one of the most egregious cases of foisting off costs on others. If you get a toxic block, find a creative lawyer and sue the former assignee for fraudulent transfer or something. Regards, John Levine, johnl@iecc.com, Primary Perpetrator of "The Internet for Dummies", Information Superhighwayman wanna-be, http://www.johnlevine.com, ex-Mayor "More Wiener schnitzel, please", said Tom, revealingly.