The letter is just a page and says that these economists are against software patents and their reasons. It makes passing reference to some studies that aren't quite on point, and doesn't provide data as to the effectiveness (or destructiveness) of software patents. There isn't even an argument as to what the goal of the software industry is (profit, access to solutions, sustainability?).

Honestly, the letter sounds to me as though we should believe them because they are the undersigned.

Just my two cents.

-David