Again, you miss the point: Paramount has no authority to affect what the fans accept as canon or not. It simply doesn't apply to us, only to their staff and licensees. There is no penalty if the fanbase turned it's back on, for example, Voyager and declared it "non canon". There is no holy-writ in place, not fandom damnation. The only people bound by edicts of canon are licensees and production-staff.
You are the one missing the point here: it is
irrelevant "what the fans accept as canon or not". The canon is defined by Paramount, as the authority figure here. It is what they say it is. Your concept of the
Star Trek universe, what you want to accept as part of it or otherwise is entirely up to you, but it
has no effect on the canon!!! No, paramount don't 'enforce' the canon by bringing hellfire and damnation on those who say otherwise, but that's because it's the fictional 'histroy' of a TV show, not a religion or a national law. An example of factual authority; I can say Sheffield Wednesday Football Club won the Premier League in Britain last year. It isn't remotely close to true, and the ultimate authority telling me that is the Football Association. I will suffer no sanctions by believing something else, but I'm certainly not right.
As far a canon being set in stone, the shows can even maintain a level of internal continuity and canon, much less something on the level of the overall franchise. How much "canon" has be contradicted over the years? How much retconing has 'Trek had to do in order make all the various abritary moments in the stories lock into place in some sort of chronological order, that was never intended till someone realized "hey, we can make money on doing this".
Actually,
Trek's continuity as a whole is excellent, given the ludicrous amount of it that's been made. But once again you are confusing a canon with continuity.
Enterprise and TOS, arguably, contradict each other's continuity - pretty badly in parts, imho. But both are and have always been, part of
Trek's canon. The definition of a canon isn't altered by continuity errors within its works.
A set-in-stone canon is not a requirement for a enjoyable series. You suppose to watch a show for its entertainment value, not worrying about nitpicky little details.
In 'The Return' novel series, Kirk is resurrected, and the Romulans ally with the Borg. Onscreen, this never occurs, and
we ally with the Romulans in the Dominion war. The canon isn't about 'little nitpicky details', or minor continuity errors, it's about saying 'this story happened in the universe and thus its consequences are a part of that universe. this one did not, so its consequences are not.' Without that, a series either becomes a wildly inconsistent joke, or deliberately becomes a show without event follow through (such as
Star Trek: New Voyages' killing of Chekhov). Star Trek hasn't chosen the latter path, so a definition of canon is necessary to establish which history, which storylines, represent the 'actual' story of
Star Trek for the purposes of writing more.