Dear Okiemockingbird: I find that it is easier to argue in the opposite direction, ie. if Manufacturer A owns the patent on a certain process and is the exclusive manufacturer, then manufacturers B thru Z should be motivated to find a new process. If the patented process was public domain and all could use it, what is the motivation for change?
I fail to see the connection between the copyright of creative works (music, novels etc) and stagnation. Popular music has evolved with changes in our society, without restriction, since the 18th C. copyright laws. Authors have not been stiffled by "Moby Dick" and have been writing the Great American Novel ever sine the 18th C. copyright laws.
[Disclaimer: I have an interest in royalties derived from copyrighted music]