lj_userdoc, since it is part of user documentation, I think, but is not part of the FAQ, which is what this community usually deals with. Hence, I'm LJ-cutting it in compromise.filter.bml is designed to use the ?filter=# query string, appended to a friends-page URL, to return a friends page that only shows posts from friends in certain friends groups. (Try it out!)
Since ?filter=0 exists (to return a friends page that shows posts from all friends, in case you have a "Default View"), I think it's only reasonable that filter.bml have an option to use it. (After all, one big thing in web design is don't-show-them-the-mechanics, which in this case means that I shouldn't have to manually edit a URL to see the unfiltered page.)
(Note for the unaware: ?filter=# is only for the user himself when he is logged in; if you visit http://ruakh.livejournal.com/friends/?filter=#, you will only see my Default View, since I've marked it public. This is a major source of irritation to those who try to use Semagic's friends-page filtering while logged out on their browser . . .)