I mean, I agree with the specific case, but I really don't see how entirely disenfranchising a political party for the views they
usually espouse isn't a slippery slope that leads to non-democratic results (i.e. major parties being silenced; or one government being arbitrarily declared "legitimate" while another is declared "illegitimate.")
Note: I'm not talking about censorship of individual posts they make for the views expressed in those posts. That's what Facebook was doing here, and I fully support that. (I'm from Canada; the concept is enshrined in law here!)
I'm just talking about the idea that you probably don't want third parties like Facebook to be responsible for deciding whether to censor people, rather the much "safer" question of whether to censor individual posts. Especially when those people are current political candidates, and the people calling for their de-platforming are people opposed to their election, who are perfectly willing to libel them if it silences them at a time crucial for swinging an election.
Facebook, unlike a government, does not have a concept of due process, and so is not equipped to deal with complaints from people who have motivations (like swinging an election) strong enough to be willing to "take it in the chin" for libelling someone, as long as their libel causes the desired de-platforming effect at just the right time.
This is why we tend to want censorship to be a legal matter: courts have well-built, well-thought-out mechanisms to allow the recipient of a complaint against them to fight back. Meanwhile, what kind of arbitration system does Facebook have? Or, more abstractly, what kind of arbitration system are they required to have? Are there any requirements at all, for how Facebook and other networks should work with people, when others are asking for them to be de-platformed?