Your rights to
use Paul's software are protected by a power
higher than his (or my, or your) opinions/beliefs/speculations
about anything.
RMS aka Saint IGNUtias?....
Actually, I saw that statement on the ZynAddSubFX site and assumed it
was an extra clause in addition to the GPL. As Paul owns the
copyright (which I assume he does) he's entitled to add any extra
licence restrictions he likes to his own software, as a 'GPL plus'.
That might mean it's not strictly 'software libre' of course, but Paul
does say 'please' rather than 'you may not use' though.
I'm unsure how the heavy metal clause is measured against, or
enforced. We're not Satanists here, but the guitar riffs can get a
bit heavy sometimes.
Cheers
Daniel