Last I checked, that is where the NDP policy stands, and we have on utube, Jack Layton talking about it in (I think) a 2008 election campaign. I also believe that the Greens are also decriminalization and so on, so the Libs aren't "leading the charge" in this regard.
Mulcair has said he doesn't believe in legalizing marijuana, but doesn't believe people should go to jail for possessing small amounts of it.