Good point, generally. However, it depends on the list or the tactic that's used. Blacklisting an ISP's ASN or entire network range because the blacklist creator set an arbitrary threshold of acceptable number of spam activity from 1 or more IPs. I'm really not sure about the legal aspects here, but there are so many practices that blatantly approach extortion. And it's skillfully done in the name of "online etiquette" or a "safe internet".

Obviously, legitimate use-cases exist for such services, provided that they are operated by faithful people/entities with some level of credibility.