What part of advocating beating children flew over your head? Michael Pearl called it a "magic wand". He advocated not only beating the children but making them pick out their implement of torture, inflicting not only physical trauma but psychological as well.
Did you not watch the CNN video at the beginning of this thread? "Lydia was so severely beaten she died of a condition normally associated with earthquakes and bombings." When asked what would cause the Schatzs to beat, terrorize and torture their children Mike Ramsey, the district attorney of Butte County in northern California, had this to say. The book by Mr. Pearl. There's no doubt about that.
There is causation that beating the child, in a manner advocate by Mr. Pearl, led to the child's death. I think I've just proven a link to any sane, rational human being on the planet.
The Pearls have sold hundreds of thousands of copies of their book. There's been only a handful of deaths caused by people who read those books, as far as I know (correct me if I'm wrong).
People who buy and follow the advice of the Pearls are likely to already be people who would resort to beating their children as punishment. Children being beaten to death happened before the Pearls published their book. Presumably some would still have happened regardless of the book being published. And they would have happened to people who are likely to beat their children, obviously, which are the Pearl's audience. So, it's perfectly possible that in a hypothetical universe where the Pearls never published their book, this same deaths happen to the same people, meaning that in fact the Pearls did not cause those deaths.
Now, this is only a sketch of an argument. I don't have the numbers of deaths due to corporal punishments before and after
To Train up a Child was published, so it could be that the numbers increase substantially and only among Pearl readers. The point is that the information presented is not enough to establish a causal link between these deaths and the Pearls, so it's hasty at best to talk about removing their freedom of speech.
(The anti-vaccination movement causing deaths, by contrast, has been clearly established by comparing deaths due to preventable diseases now and before among populations with access to vaccines.)