In those days, people watched what they said. Public cursing was seen as being disorderly. Kids were careful how they treated the teachers, and teachers were careful about the directions that they led the developing minds. I never heard about anyone smoking marijuana, let alone saw anyone do it.
At that time, a book on how to make bombs, or how to shoot up a school would not have seen the light of day. There are some things that simply are not in the best interests of the public, and need to be suppressed from public view. Our courts have just let the "freedom of speech" tread off into the neverlands that are not fit for decent company. And the route was laid out by liberal anarchists for them to induce the reign of terror, at the end.
Where an anarchic, free-speech, terrorist-breeding sphere of activity has been allowed to develop by a dying society, there is a place for returning to burning some kinds of books, IMHO; as well as jailing their authors and publishers and confiscating their profits.
How free is "free"? I do not think it is freedom to act just any way one wants, to the harm of many others, nor do I think it was the intent of our Founders and their followers.
As I said, the New Zealanders may have gotten hold again of some kind of effective reason for preventing distribution of hurtful information.
Bomb making books were available at that time, as was widespread access to explosives.
Up until 1968, anti-tank and anti-aircraft cannon and ammunition were available by mail order.
We had crime levels about the same as we have now.
What we have seen is the glorification of mass murderers by the Media (giving them fame after their deeds).
We have seen wholesale derogation and rejection of Christian values.