You can see them in WW2 photos. I wrote an article on it:

https://battlepenguin.com/politics/paint-the-sky-with-clouds/

I did seriously consider this before I started traveling around the world. They're not spraying in the middle of nowhere South Australia between the 1,000km stretch of road between two tiny truck stops.

I don't think people are dumb for believing in chemtrails, and there are documented reports of cloud seeding by various governments, however what you see behind commercial jetliners are clouds. They're thicker than the ones from when we were younger, because the engines burn a lot hotter and more efficiently.