(many hours later) ... I'm going to point out from the printer story...

https://www.gnu.org/philosophy/rms-nyu-2001-transcript.txt

    And we just had to suffer with waiting.  It would take an hour or two to
    get your printout because the machine would be jammed most of the time.
    And only once in a while -- you'd wait an hour figuring "I know it's
    going to be jammed. I'll wait an hour and go collect my printout," and
    then you'd see that it had been jammed the whole time, and in fact,
    nobody else had fixed it.  So you'd fix it and you'd go wait another
    half hour.  Then, you'd come back, and you'd see it jammed again -- before
    it got to your output.  It would print three minutes and be jammed
    thirty minutes.  Frustration up the whazzoo.  But the thing that made it 
    worse was knowing that we could have fixed it, but somebody else, for his 
    own selfishness, was blocking us, obstructing us from improving the software.  
    So, of course, we felt some resentment.

    And then I heard that somebody at Carnegie Mellon University had a copy
    of that software.  So I was visiting there later, so I went to his
    office and I said, "Hi, I'm from MIT. Could I have a copy of the printer
    source code?"  And he said "No, I promised not to give you a
    copy." [Laughter]  I was stunned.  I was so -- I was angry, and I had no
    idea how I could do justice to it.  All I could think of was to turn
    around on my heel and walk out of his room.  Maybe I slammed the door.
    [Laughter] And I thought about it later on, because I realized that I was
    seeing not just an isolated jerk, but a social phenomenon that was
    important and affected a lot of people.

    Now, this was my first, direct encounter with a non-disclosure agreement,
    and it taught me an important lesson -- a lesson that's important because
    most programmers never learn it.  You see, this was my first encounter
    with a non-disclosure agreement, and I was the victim.  I, and my whole
    lab, were the victims.  And the lesson it taught me was that
    non-disclosure agreements have victims.  They're not innocent.  They're
    not harmless.  Most programmers first encounter a non-disclosure agreement
    when they're invited to sign one.  And there's always some temptation --
    some goody they're going to get if they sign.  So, they make up excuses.
    They say, "Well, he's never going to get a copy no matter what, so why
    shouldn't I join the conspiracy to deprive him?"  They say, "This is the
    way it's always done.  Who am I to go against it?"  They say, "If I don't
    sign this, someone else will."  Various excuses to gag their consciences.

Nothing required Xerox to give Stallman the source code to the printer driver. And in a world without copyright, nothing would require Xerox to give Stallman the source code to the printer driver either. And it wasn't copyright that prevented Carnegie Mellon from giving him the source code - it was a separate contract - an NDA.

The four freedoms are guaranteed for open source because of copyright. Without copyright, the first freedom (with the access to the source code) for open source software is not possible. Copyright gives the author the ability to force others who use the software that they've licensed to be similarly open.

Consider this challenge - write a license on top of some public domain ( https://en.wikipedia.org/wiki/Public-domain_software#Public-... ) work that requires that I follow it and that the work that I do provides the four freedoms - that would prevent me from taking the code and repackage it in my own binary in a way that I'm not obligated to disclose to you or that you wouldn't be able to replace with your own library.