I do not see a problem with indefinite copyright protections. One of the assumptions is that everything being equal the same works would exist if it were not for copyright protections. However, I would argue without the extended copyright protections, most of these [future] classic works would not exist, simply because publishers/studios would not invest in the creation/distribution of the works initially. In other w…
On the one side, if you don't have copyright at all, it severely limits the ability of creators to monetize easily copied works. This became a problem with the printing press and copying has only gotten easier as technology has progressed.
On the other side, there are a number of problems with granting an absolute, indefinite copyright. One is that you stifle the creation of derivative works. Another is that obscure works can easily fall out of print and be lost forever. A larger philosophical concern is whether corporations should be allowed to hold control over the shared cultural heritage of a society long after the actual creators have died.
Almost everyone sees the need for some kind of compromise here. Personally, Canada's life+50 years sounds pretty reasonable to me.