My dad would take us to the library every week when we were kids. We could chose two books ourselves and he would choose the third one for us. There were still some books on the banned list. He would seek them out at local markets. The book-sellers who could get copies of banned books would sell out quickly and my dad always taught us that if it was banned, then you needed to read it.
If they (whoever they were at any given time) didn't want you to read a particular message, then that message may be important. So the Catholic Church would have some competition because the highest praise a critic could give a book in Russia is — “The communists would certainly have banned this.”