I am sorry, but your premise is wrong, and, AFAIR, in another thread I have shown you some examples of recent information on weather modification before. There cloud seeding is not a secret.
Have you tried looking for the impact of cloud seeding materials on the environment? I'd consider that a first step. Here's some literature, spanning several decades:
Steinhoff, Harold W., and Jack D. Ives, Eds., 1976: Ecological Impacts of Snowpack Augmentation in the San Juan Mountains, Colorado. Final Report to the Bureau of Reclamation.
Bureau of Reclamation, 1977: Project Skywater, A program of Research in Precipitation Management. However, some research indicates that silver toxicity is bio-accumulative in aquatic environments, causing respiratory distress to some species of fish (Aquatic Toxicology Volume 49, Issues 1-2, May 2000, Pages 111-129).
Howell, Wallace E., 1977: Environmental Impacts of Precipitation Management: Results and Inferences from Project Skywater. Bull. American Meteorological Society, 58, 488–501.
Donald A. Klein , 1978: Environmental Impacts of Artificial Ice Nucleating Agents, Dowden, Hutchinson & Ross, Inc., Stroudsburg.
Harris, Edward R., 1981: Sierra Cooperative Pilot Project - Environmental Assessment and Finding of No Significant Impact. U.S. Department of the Interior, Bureau of Reclamation, Denver, CO.
Parsons Engineering Science, Inc., 1995: Environmental Assessment for the Pacific Gas and Electric Company and the U.S. Forest Service, Stanislaus National Forest.
Also, here:
http://www.abc.net.au/science/articles/2010/11/09/3060615.htm
Not only is there no silence on weather modification, it is being reviewed specifically for the dangers you fear. (And that's just what I found googling for less than 5 minutes.)