The logic behind chemtrails is that evil governments or the rich Illuminati elite are intentionally spraying specific chemicals to control population. If argument was ecological impact of burning fuel, then we'd have to ban airplanes, not chemtrails. But that's not the argument.

Also it's not water droplets or vapor, it's most likely crystalized water vapor or droplets. Commercial airplanes fly at around 10km above ground and temperatures can get very low, we're talking -40°C. It's literally those videos where someone throws a pot of hot water up in the air outside during cold winter. It instantly turns into a white mist. Hot jet engines, cold atmosphere, burned fuel and vapor during combustion, would you look at that... CHEMTRAILS!

Not to mention weight is incredible luxury metric on airplanes. If conspiracy people think commercial airlines would carry half the fuel on board and replace other half with chemicals for chemtrails, because reasons, yeah, they don't do that. They actually rather not even fill the fuel tanks all the way if it's not necessary for the flight and rather do it when airplane touches at the destination and they refuel it there. Because carrying additional weight consumes more fuel, even if that weight is the fuel itself.