1) In my view the primary reason to drastically shorten copyright is so that it is easier to create new works. For example, documentaries have startling problems due to copyright, see for example http://www.nytimes.com/2005/10/16/movies/16rams.html?_r=0

2) Isn't someone who holds a copyright other than the creator (say in this example the Conan Doyle estate) profiting from the work of others?

3) Like all sensible issues, deciding the proper term of copyright should be understood as a set of tradeoffs. Longer copyright terms may encourage more creative work by increasing the payoff, may give authors more creative control in how their creations are used and so forth. Shorter copyright terms may encourage more creative work by reducing the cost of remixing other's ideas, can provide a common pool of cultural resources for all to draw on, and so forth. What is necessary is to try to balance these competing interests against each other. It is not that shorter copyright terms are "automatically better", but I (and apparently many others in this thread) strongly believe that the balance right now has copyright terms that are too long to be socially beneficial.