Re: Using of parse tree externally

[kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)]

    My wife believes that software can be licensed with the restriction
    being discussed, and that such a license could be enforcable without a
    signature.  However, I believe she's talking about a softare usage
    license by the copyright holder (the FSF), rather than merely a
    copyright license.

Exactly and that's the critical distinction here.  The GPL is, in essence,
from a legal perspective, two documents: a license agreement and a waiver of
certain copyright rights.  That kind of restriction would be permissible in
its first role, but not its second (more, precisely, as others have said, the
restriction is either already there or is not permitted to be added,
depending on the details of copyright law).

It's the second role of the GPL that's the important one.  One reason is that
there are statutory penalties for violation of copyright, so it has "meat".
As a license, it would be a contract between the FSF and the user and there
are two problems with that.  First, because no money changed hands, it's not
at all clear such a contract would be enforceable at all and secondly even if
it was, the FSF would have to show economic harm before it could collect from
an infringer and that's going to be nearly impossible.

So you may gotten the right answer to the wrong question!