So what is the cause of this generic "stress"?

I don't think it's appropriate to give any simplistic answer to "what is the cause of this generic stress?"

I do see a combination of complex issues at work here. For many kids, school is a big source of stress. Kids are told success in school is the only route to having a happy life and they can't see past the lie. Being put with same-age peers in large numbers creates a lot of social issues that cause stress. Loss of close family bonds is a source of stress. Being raised to be materialistic and looking to constant entertainment for "happiness" is a cause of stress. Having meaningless, purposeless lives by being confined to meaningless busy work in school, as Gatto talks about, is a big source of stress. My 21 yo tells me lots of her age peers also think the society we have created is headed for catastrophe, we just can't sustain this monster we have created. That is a source of stress.

I work with a number of square peg kids after school in private language therapy and several are on anxiety meds, OCD meds, etc. One boy who has a lot of language challenges obsessively computes his grade point average with a calculator in his free time at home. He said he's working on stopping doing this.

Lots more ideas here, but lots of kids are under a lot of stress from what I can see. Not that life was meant to be stress-free, but when you start getting suicides and dysfunction in large numbers it should set off some red flags.
Leslie in KY

I just found the word "stress" to be simplistic, that's all. Sorry.