People have been suspended or banned for "misinformation" ranging from Covid treatments to perceived irregularities in the 2020 elections. The New York Post was censored by Twitter for its initial report on the Hunter Biden laptop, which was subsequently verified as factual. There are countless other such examples. Heck, a friend was suspended from Facebook for a political posting months ago, and he still hasn't been able to find out why.
I don't want to defend Facebook or any social media platform. I'm sure they are often wrong in who they ban.
But it makes sense to me that spreading misinformation about vaccines is a good reason for getting you banned. Vaccines are a matter of life and death not just for people who get vaccinated or not, but to everybody to whom they can spread the disease. If you tell people not to get vaccinated and they believe you, you put their lives in danger.
Similarly you can be prosecuted for shouting "Fire!" in a crowded theater causing people to panic and die being trampled and crushed. You could then try to argue that "It is just my opinion that I have the freedom of speech to shout 'Fire' anywhere and whenever I want to". But courts are not going to agree with you.