I and others have written several articles on this website about the anti-vaccine hate debate – discussing the atrocious and hateful behavior of a large portion of the anti vaccination cult.
This kind of “free speech” goes beyond simple mockery, ad hominem attacks, or, though it rarely happens, arguments about the science. Ad hominem attacks are, by definition, personal attacks that are used in lieu of real evidence. So, if you lack evidence to support your side of a debate (even a fake debate like what is happening with vaccines), you attack the person, rather than the evidence.
Of course, if you do lack evidence, you will be mocked mercilessly for lacking said evidence. Cherry-picked evidence doesn’t count. Appeals to authority as evidence doesn’t count. Employing the Nirvana fallacy doesn’t count. The only evidence that matters must come from high quality sources that are repeated many times and are often rolled up into a substantial meta-review.
The vaccine hate debate on exists because they have nothing – no evidence of harm, no evidence of a lack of benefit. None. Ground zero of the Facebook anti-vaccine hate crazies is The Vaccine Resistance Movement (VRM) – read their hatred and lies. Donald Trump would be proud of them.