The difficulty with all conspiracies is us !. Humans have grown to be sceptical, so sceptical we are even sceptical about the sceptics !.
Firstly I must point out that most of the white streams trailing behind planes is a nutural occurance of vapourisation.
But there are theories that they are also purposely spraying chemicals, in attempts to control the weather, for the purposes of mind or behavioural control of the population, chemical warfare or for mass depopulation.
Look at the evidence and make up your own mind!
Credit to: Justin Wallis
Credit to: Studio 10
Credit to: Captain Joe
Credit to: Planting Freedom - athatcher85