The public domain still exists. It's functionally equivalent to a right to piracy, and is written into the constitution. Note the phrase "limited times":
U.S. Constitution
Article I Section 8 | Clause 8 – Patent and Copyright Clause of the Constitution. [The Congress shall have power] “To promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries.”
No one is claiming that accessing media that is in the public domain is piracy. We are specifically talking about media that is not in the public domain.
I think the idea is that we wouldn't need piracy if media would enter the public domain after a sensible amount of time. Now that disney + sony are essentially legislative branches of the us government we can be sure that nothing of value will enter the public domain ever again.
The first amendmend does grant you the right to free speech, which "piracy" is.
The constitution also allows the government to limit that right "To promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries."
There are quite a few limitiations in that right that current copyright laws arguably go beyond.
