If you'd like to check weather balloon data, you can explain to me why, on the hottest day of the year (up to that date) August 16th 2012, the following mess was observed at around 1:00 pm, the hottest part of the day itself, directly over London; over Covent Garden in fact. Now, I lived in London from Oct 1978 until Dec 1992 and I never once saw anything like this, winter, summer, autumn spring. If even a single plane had left marks like this, people would have been very alarmed.
At around 9000m the temp was -42 and pressure 314, with 37% relative humidity. The appleman chart says contrails are not likely under those conditions, but we watched as these things drenched the sky in short order. If you like your skies this way, then you're quite right to shout down anyone who complains. But if, like hundreds of thousands of sane people, you like a blue sky every now and again, you're going to be saying - WTF?!