This is the heart of the issue. Just because legitimate and identifiably bad advice exists doesn't mean this is suddenly widely applicable to all health information. Youtube isn't banning content that the WHO is "absolutely certain is true" either, they are using any of the (frequently changing) general advice coming out of WHO.
There's always tons of grey area on what is true or good advice. No matter how much 'science' is thrown around, or credentialism ("they have a PhD!"), or credibility some international organization has, that does not make this any less true. Especially when it comes the speech of the general public - not some advice via some formal expert forum or government body.
Even Snopes.com is littered with incorrect and politicized positions, and unlike the WHO, their actual stated goal is trying to determine what is true or not. WHO has a million different incentives beyond this.
What is useful advice for governments to disseminate, given tons of competing interests (which is what WHO specializes in), doesn't automatically translate to what regular people should be allowed or not allowed to discuss in an open forum.
Additionally, we're not being asked to just trust WHO to have good advice and good intentions, Youtube is telling everyone to trust WHO information proxied via an Youtube moderation teams interpretation of it, via an opaque no-appeals process.
Anyone who has used any major platform before (Reddit, Paypal, etc) knows how stupid moderation teams can be. And the vast majority of moderation teams haven't been stupid enough to try to determine what is 'true' or not. Because that's crazy.
The only way I might support this is if it helps bring about the demise of Youtube.
I don't have an opinion on whether it's true or not myself. I’m not qualified to say.
I just know that reputable authorities disagree on it. So how can you enforce a truth here?