Re: RMS: users request you perhaps program HURD: they fear the path the linux kernel is going.

[Richard Stallman]

[[[ To any NSA and FBI agents reading my email: please consider    ]]]
[[[ whether defending the US Constitution against all enemies,     ]]]
[[[ foreign or domestic, requires you to follow Snowden's example. ]]]

  > Please forgive my ignorance, but what's wrong exactly in licensing
  > under only a single version of the GPL?

That creates a license incompatibility.  GPL 2 and GPL 3 are
incompatible licenses.

For instance, suppose you want to merge code from Linux (released
under GPL 2 only) with code from GCC (released under GPL 3 or later).
There is no lawful way to do it.  GPL 2 and GPL 3 have requirements
that conflict, so there is no way to satisfy them both.

If Linux were released under "GPL 2 or later", there would be no
incompatibility; merging code from Linux with code from GCC (or any
other program under "GPL 3 or later") would be possible.

See https://gnu.org/licenses/license-compatibility.html.

-- 
Dr Richard Stallman
Founder, Free Software Foundation (https://gnu.org, https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)