Every nightmare has an origin, you get chased by a dog, and you dream one up as REM cycle does it's memory dump, and you see something similar in your dream.
The conspiritards are similar, they hear of a legitimate problem, and run around screaming of it, not knowing when and if it really happened.
Chemtrail if fueled by many "thoughts" ranging from population control to reflecting the sun's radiation in an attempt to cool the earth, or "replace" depleted ozone with an artificial barrier. All kinds of $*!+ is floating on the web.
There was however a possible spark to fuel fear in bored people that know that everything on the web is true, and it was Operation Popeye. Among other effed up things that happened there, this one was a chem-trail geoengineering thingamabob.