I have no opinion about the validity of either case. I don't know enough about other things planes could be doing - cloud seeding, for example. I find any explanation just as likely, and the idea of a stutterer hiring a sky-writer tickled my funny bone. I apologise if I offended you.
I am near impossible to offend, taking offense requires that I have some sacred cow which cannot be challenged, and I have no beliefs so closely held as to trigger that level of response, save one, that no person has the right to initiate the use of force, the threat of force, or fraud against another person or their property. If you challenge that, I am disgusted, not offended.
That out of the way, cloud seeding is a valid, and non-nefarious, explanation of "chemtrails," but I have to wonder, were it just that, why wouldn't they just say it, instead of all the secrecy and denial?
possibly because cloud seeding could be used to rip off people who buy weather insurance.