But it isn't fact checking. It's opinion censoring. Now that doesn't mean it shouldn't happen but presenting it as objective is simply a lie.
It is much, much more complicated than that.
People on social media rarely say 'my opinion is X, or Y' - indeed 'opinions' are often not overtly voiced at all - they are hidden in a kind of dog whistle way around claimed 'facts' which may or may not be actually true. And those claimed 'facts', often also selectively picked (inconvenient facts which do not support the opinion and agenda of the poster are conveniently ignored or not amplified).
Indeed problematic posts may do nothing more than share someone else's claimed fact, without giving (overtly) an opinion whatsoever - although the sharing of the post speaks volumes about the 'opinion' of the sharer. And that's why it really is important that the facts are just that - facts. Not fake news purporting as true etc as that 'fake' news is used to drive opinion.
So if someone simply shares, retweets etc a claimed new story that 100 children were killed in Gaza by an Israeli air strike on a hospital - it is likely clear the opinion of the person making that choice to share/retweet, although they may voice no opinion in their post whatsoever - merely claiming something as 'fact'. And it is important therefore that the news, the facts so-to-speak, are actually true.