There is a big time conspiracy theory about something called "chemtrails". This conspiracy theory is based on the belief that contrails coming out of a jet's exhaust are laced with chemicals that's propose is for population control.
There are several problems with this theory. First, there is no proof what so ever that what a person sees coming out of a jet exhaust is nothing more then a contrail, rather then the "chemtrail" that so many conspiracy theorist insists that they are. In fact, not one pilot, or any other person who would be involved in this alleged conspiracy, has ever even come forward and said that the government was spraying chemicals on the population.
Besides the fact there is no proof, spraying chemicals from two to three miles above the ground isn't a very effective way to disperse chemical or biological agents. The wind from that high up would disperse the chemicals and biological agents throughout the upper atmosphere, and it would become so disperse that when or if it ever did come down, there wouldn't be enough of the stuff to be effective. Take a look at crop dusting for instance. Crop dusting planes have to be very low to the ground to spray fertilizers and pesticides in order for them to get on the crops. It can't be done from thousands of feet in air, because the wind would just blow it away.
Another claim is that "chemtrails" are responsible for causing multiple health problems, mostly respiratory illnesses. The problem with this, is that there really is no way to prove that what is causing these respiratory illnesses is nothing more then either air pollution, or smoking, or an infection of some kind, or life style habits, or just something a person was born with.
The fact of the matter is, there is just no proof that these so call "chemtrails" are real. Every study ever conducted by any legit organization has concluded that what is being seen is nothing but contrails. Sometimes these contrails just react differently depending on the atmospheric conditions. Besides, if they were spraying chemicals, as is so claimed, then they would have to fly a lot closer to the ground to make the stuff effective, and a lot more people would be getting sick, and the population would be shrinking. In fact, the population of this country, and the world, is growing. So if these "chemtrails" really are real, they're not effective at all...