Okay so obviously the chemtrails people are nuts ("THEY" are dosing us with EXPERIMENTAL CHEMICALS and HIDING THE FACE OF THE SUN AND SKY to PACIFY AND DEMORALIZE US!) but I think one thing they harp on is actually pretty interesting: aircraft contrails can be very persistent, and if you live in a place where air traffic has increased by an order of magnitude over the last 70 years... the sky may look super different than it used to (depending on local climate and weather etc).
Imagine if air travel started today. The NIMBY/environmentalist backlash would be apocalyptic. You'd have liberal activists coming out from under rocks to say how the native tradition of venerating Father Blue Sky means that any change to the appearance of the heavens is racist and illegal! Every podunk hamlet in Montana and leafy suburb in "one of the 50 highest-earning zip codes in the US" would be a nonstop war zone as the local city councils try to establish a no-fly zone between the ground and the Kármán line! Papers about how the endangered eastern dung beetle relies on subtle natural sky color striations for wayfinding on their epic continent-spanning migrations would make the front page of the NYT!
One could argue that that situation would be better than the status quo, but either way I think it's interesting that, instead of holding a society-wide Contrail Thunderdome, we've taken all the people who care about the appearance of the sky and put them in a little containment chamber of 90s-era conspiracy forums and the gross part of Twitter.