If linking to copyright infringing material is infringement itself, then it surely must be infringing to link to material that is linking to copyright infringing material? Otherwise Piratebay could just give pointers to 3rd party services that host torrents that point to infringing material. (Well, magnet links could be considered links to torrents that link to warez.)
But that technically leads to a situation where you can't link to any site that could host links (to links) to infringing material. Mention piratebay.org -- oops, a link. Or you previously linked to some site that now has these copyright infringing links. Boom, you're infringing copyright.
That might be nerd's thinking but you really do have to have the line drawn somewhere because laws must generally be well-defined. You can't have a gray area where legality of something depends on the whim of the case. Linking is either illegal or it isn't, and if it's illegal it must be clear what constitutes linking.