Howard Knopf is right of course in his objection at EXCESS COPYRIGHT: Just Say No to Copyright Term Extension – Why More is Less: My Views on #TPP.
But I would go further. No copyright on any work should ever be extended beyond that which was in place at the time of its creation.
Not only is it obvious that no such extension of copyright can add any incentive to the creation of the work, but the extension is also actually an act of theft – first from the public whose rights are given away, but also from the creator (and any previous owner) who sold the work for a price based on the copyright term in effect at the time of the sale.