This is a very long-standing and AFAIK never explicitly decided copyright and human rights question: If something is Public Domain, are contracts restricting distribution valid? Is our right to information or knowledge a fundamental human right that is not permissible to take from others, such that restrictions greater than those imposed directly by the State are invalid? In a healthy society, "I have created an extraction machine and your actions are hindering my extraction" is not a valid argument. So at the very least contracts restricting rights to public dmoain works should be allowed only with heavy restrictions as to when, how, and for how long they are binding - much like the legality of non-competes have has steadily reduced in many places in recent years.

CC0 came about in part because of this ambiguity. To deal with it, part of CC0 basically says - even if there would still be restrictions to this if it were only in the public domain, I renounce those theoretical rights.

Outside the underdeveloped legal framework, I believe knowledge and truth is like life, and human society has some continued philosophical growth required here.