I found your link to Zublick's video very interesting, but gently point out that his claims and assertions have no "hard evidence" to back them up.So if you want to use hard evidence as a guide to permissiveness in what one can say, I suggest you apply the standard to everyone; though for a lot of subjects, there will be nothing to discuss, because a lot of people hide their deeds and we cannot present hard evidence for every statement we make.
We are not in a courtroom.
Circumstantial evidence is also evidence.
Sometimes it is all we have to form an opinion.
