With the filtering lists of Australia, Finland, Denmark and Thailand all leaked onto the internet there is no longer valid argument to not punish the IWFs list, it wont provide any greater resource of CP links than those already leaked. It is surprising the UK list has not leaked yet - during the wiki fiasco it was disclosed that someone over at Be* could view the list (even if they weren't supposed to) so I guess its only a matter of time till a less trusted ISP signs up for the service.

Publishing the list is similar to the police producing a map of areas with prostitutes or drug dealers - I don't have to go there myself and use their services but I can complain if I live near / visit the area and think the information is incorrect or they are no longer there.