CBC has the power over its own Facebook pages, and it operates under a set of social beliefs about what constitutes hate. Why shouldn’t they decide they don’t want to deal with people who, in their eyes, have no valid point to make? We can criticize CBC’s decision as idiotic or foolish, but I think they hold a right to prevent discussion their standards do not allow.
Because CBC is in the business of convincing its audience they have a valid point to make, not the other way around.
There's tons of ways to break down media-as-an-information service, but one way is to break down audience perception of media into three forms: 'media intended to inform,' 'media intended to convince,' and 'media intended to indoctrinate.'
Again, these are breakdowns of an audience perspective, not producer intention.
Media intended to inform in this context is (moral) conclusion neutral. It doesn't particularly care what moral opinion you the audience form, it's just there to give information. That information doesn't even have to be unbiased or without motive of affecting a person- an emergency alert is directly seeking to have you take shelter, for example- but the bias is usually explicit/conveyed as part of the information. A lot of advertisements fall into this category- they can be manipulative to varying degrees, but fundamentally they're media meant to inform you [product exists; can do these things] and the only moral judgement involved is if it helps your problem. At the same time, though, because no argument position is being made, no audience engagement is really needed. The add commercial doesn't care if you agree or disagree- it wants to sell, not have a debate. Similarly, sports stats are for the stats, not a discussion of how they should be interpreted.
Media intended to convince is media that, by design, wants to convince people of a position or interpretation. But from an audience position, this is a two-way street, with some form of push and pull over 'why.' The media can bring up points it thinks are valid, but to convince someone that their position is wrong it has to address the points the audience thinks is valid. The nature of the medium may make an exchange impossible in practice in real time, but this is why political debates have so many different forms even in written media; a lot of newspapers editorial sections have (used to have?) sections for publishing pro/anti- opinions side-by side, or report transcripts, or publish letters to the editor disagreeing, and so on. Fundamentally, media to convince a person needs to address points that the consumer feels are valid.
Media intended to indoctrinate doesn't care about addressing the points the audience thinks is valid, and thus functionally isn't about convincing the consumer 'why' to think as much as directing them to 'what.' Making arguments is a useful utility in so much that the audience is converted/reflects the desired endstate, but then lying can have the same effect. Functionally - from the audience and producer perspective- it doesn't matter if the audience is convinced, deceived, or intimidated into compliance as long as it complies. Obviously a lot of media can't actually tailor threats to the audience, usually, but from the audience perspective 'media intended to indoctrinate' is aimed at a result, not at persuading the reader (even if it might try to do so).
The thing is, and the reason why it's useful to break down the audience-centric calssification even though type 2 and type 3 media can have the same motive/objective from the producer (to get people onto the desired position), is that type 3 media really truly and broadly is terrible at actually, well, achieving the producer's goals of converting people to a position. There's a reason why the term 'propaganda' is such a pejorative when it comes for media- it's a catch-all for media who's primary interested at aiming at, not engaging with, a listener, and produced by people who either don't care about truth or may not even know it. The audience's perception of being either the target of persuasion, where persuasion is the goal, or indoctrination, where persuasion is just a means, is one of the quickest factors of terminating audience engagement, willingness to entertain good faith, and not just being convinced but even paying attention. 'Paper fit only to wipe your ass with,' and all that.
And one of the quickest ways to see if the writer is interested in engaging with you, or talking at you, is if they even pretend to be willing to engage feedback. Is there a forum or space to point out mistakes and failures of arguments? Will the writer or medium address them if pointed out? If a medium won't even entertain that it's wrong- and journalists are just as mediocre generalists or blind to nuance or bias as anyone else- it's a strong indicator that truth and convincing is not their main goal.
CBC, like a lot of media, is filled with people who want to be taken seriously. If they're anything like the medium mainstream media outlet, they're also packed with journalists whose ethos entails some form of 'want to make a difference' or 'help people by making more informed decisions.'
This doesn't occur if you're written off as a propagand. Closing comments and feedback does more than cut off harrassment and personal attacks- it cuts off a major distinguishing feature from being type 3 or type 2 medium. Media aimed at convincing may not address feedback, but propganda will never publicize and systemically minimizes facts and context that undermine the desired conclusion. If your own audience doesn't feel they are allowed to point out relevant facts or context they feel are relevant...
If CBC wants to be be taken seriously and believed they have a valid point to make, they have to convince the audience they're actually interested in valid points, and not just propaganda. Comments - even if rarely engaged - help with that audience buy-in.