The filter is a safety net to catch the worst of it and can't serve as complete censorship in the way it would need to for it to actually replace that rule. People will still find ways to bypass it, even by accident with a typo, and it doesn't make the language any more appropriate for a public channel.

My language in linkshells among friends is not appropriate for public chat and I think it's more than fair for there to be rules enforcing that, since public channels should be comfortable for everyone and language like that can come off as pretty hostile to players who don't use it so lightly, especially through text.