As far as I know, it was never illegal in the USA to own a copy of Mao's "Little Red Book". I know this because I bought one, on open sale, from a bookstore in Berkeley back in the late 70's.
I thought it contained some interesting bits of general wisdom, along with hopelessly trite political propaganda. My favorite:
"Quantity has a quality all its own".
And on that basis, the US Tank Corps overwhelmed the Germans in WWII.