The banning of public speakers and creation of "safe-spaces" is the next step to society wide censorship. Why should someone else get to decide what ideas I can and cannot hear? Freedom of speech is vital as there was a time when it was illegal to say the Earth orbits the sun. Having said that, freedom of speech does not include the right to be heard. You should be allowed to say what you like (provided it is not illegal) and you will be ridiculed if what you say is stupid.

Indeed, the rights that give you the freedom to talk nonsense (such as anti-vaxxers) are the same rights that give others the freedom to criticise, ridicule or completely ignore you. Just as freedom of religion includes freedom from religion, freedom of speech includes freedom from speech.

I think the issue that you refer to is actually due to the internet. Quacks have always existed, and they have always been rightly ridiculed. Before the internet, that was the end of it. Now they can find each other too easily, organise in to groups, and spew their nonsense to a wider audience.

Ironic that the internet gives them more access to information and evidence than ever before in human history, and instead they use it to spread their ignorance.