I have found that there are basically three main viewpoints on the reasons for chemtrail spraying. Correct me if I'm wrong anyone, but the first is that the spraying is a defense against foreign powers who are experimenting on weather control, or environmental control-based weapons, and the chemtrails are used as a sheild of sorts. The second id that this is a mass-vaccination or slow wear-down of our systems to weaken the population's immune powers for when "they" release a plague of sorts to wipe out many many thousands, if not millions, a.k.a., polpulation control. The third is what you have stated in your post, John.
MH, Vandy, & anyone else who knows, based on all the information you posess on the subject, which of these scenarios is most probable? Or, is there a lot more to it than this simple overview? It seems to me that no-one really absolutely knows why this is happening, but I have sided with one of these theories.