ISPs are not the police. They can decline to offer a particular service (protocol) such as SMTP, but they must never be given the responsibility or authority to make judgment calls on access to particular websites.
Following on from your suggestion, I know of a blogging platform owned by a very large search engine which is overrun by automated signups and fake spam blogs, offering dubious downloads and such. The blogs are all subdomains of blogsp.. I mean example.com, so I assume it is OK in your book that individual ISPs take matters into their own hands and block access to this service?
Of course, there are a few legitimate users of the service, but they are merely people who are too cheap to plunk down a few $'s a year for a service now given away free, so no great loss. ;)