The other big problem with these schemes is the idea of exponential growth. If everyone participated for just five iterations of the scheme, it would generate 3.2 million letters (20^5) - approximately the population of the united states. A few more generations and the world would literally be buried under mountains of paper.
Clearly unsustainable.
Exactly, and with the mailing lists getting reused the same people would be receiving multiple letters. Clearly not going to work.