Recently, Nina "Sita Sings the Blues" Paley and I conducted a protected email exchange debating the merits of the Creative Commons "noncommerical" licenses (like those used on my novels and here at Boing Boing). It was an instructive and sometimes productive debate, and Nina's edited the thread and posted it.
Here's my perspective: the purpose of any cultural policy or regulation
should be to encourage a diversity of both participation and works (that
is: more people making art, and more kinds of art being made).
ISTM that your assertion amounts to: "Whatever forms of participation
that come into existence as a result of the capitalization opportunities
that accrue in an exclusive rights regime, they are dwarfed by the works
that lurk in potentia should such a regime perish."
IOW: we unequivocally get *some* participation in culture as a result of
exclusive rights regimes, some of which would not exist except for
exclusive rights. You believe that if this regime and the works that
depend on it was to vanish, the new works that would come into existence
as a result would offset the losses.
I don't know how either assertion could be tested. We both have
firsthand experience of both modes of creativity -- I know of works that
wouldn't have been capitalized absent the higher returns expected in the
presence of exclusive rights; I also know of works that could only have
been made in their absence.