Then the interface won't be more complicated after all :)

OTOH, I don't think it's quite as easy as that. The writer probably needs some way of saying "These are official tags you may want to filter by," (either just by posting that, or a list of such tags like the current list of filters), otherwise the reader won't know that the tag is guaranteed to be used, and not to be used on posts with nontagged stuff as well, etc.