It's from an an essay written as a hypothetical commencement speech by columnist Mary Schmich, originally published in June 1997 in the Chicago Tribune.

Then released in several versions as a spoken word song by the Australian director Baz Luhrmann.

https://en.wikipedia.org/wiki/Wear_Sunscreen

It reached peak parody when further mangled and released by John Safran as Not The Sunscreen Song https://www.youtube.com/watch?v=8YwqFz14xY4

It was Mary Schmich and later Baz Luhrmann turned it into a song: https://en.wikipedia.org/wiki/Wear_Sunscreen

Vonnegut had nothing to do with it, and it doesn't preclude that there really are changes that slide one way or another, in fact when I was a kid compared to the wages of the day many prices were more reasonable than they are today, many politicians were in fact much more 'noble' (though that word doesn't really fit) than they are today. As to whether children respected their elders or not I have no opinion on but the other two definitely have shifted where I live, the kind of rabble that sits in parliament here today would never have gotten a pass in the 70's. FFS we have a guy here that believes that lizards rule us.

https://www.lemonde.fr/en/international/article/2022/10/21/d...

The fact that enough people vote for these characters has me more than a little bit worried. Democracy is super fragile and to wave away the observable fact that in the past things were quite different by quoting some random text seems to be a bit too glib and easy.