keep in mind there are hundreds of other IRC clients with filesharing abilities.. are they also not illegal? What about usenet clients? The abuse of a protocol does not automatically make the software that is used to abuse it illegal, especially not when it is not condoned by the author or community.. this is the opposite of bittorrent, for instance, where the author might not agree, but the community certainly thrives off of illegal filesharing (thepiratebay and all the previous sites that have been shutdown).
There is actually a lot of IRC activity that has nothing to do with filesharing-- and if you haven't yet seen any of it you should start looking around more.
