I'm actually willing to accept the argument that copyright term should be independent of the life expectancy of the author -- that does affect the perceived present-value of the work. It's also how copyright was initially construed: a 14 year term, extensible once. Later extended to 28 years, with one renewal (by the author or heirs), to a maximum of 54 years.

What I don't support is for the term to be either indeterminate (as the repeated extensions of the past century have established), or perpetual, or even particularly extended. There are only a small number of cases where a 50-60 year term wouldn't be sufficient, and the concept of an extension means that unvalued works would enter into the public domain quickly.