This guy had bad back problems and got surgery but it was probably ongoing. He got kicked off his parents insurance at 26 and ran out of money.

He was working for TrueCar as a data engineer, he had employee provided health insurance.

This sounds ridiculous, given his family background, from which running out of money seems unlikely, but it’s actually plausible. I know a lot of people who came from wealth but who insisted on fighting their own battles. I personally wouldn’t recommend it, though.

Most folks with mental illnesses live among us, not in mental institutions. If on a scale 1-10 you have something like bipolar on 1 or 2, you can sort of function with some meds. Sort of, until SHTF and emotions go haywire. Keeping relationships is hard, be it personal or professional, so folks struggle but from outside they often just appear 'weird'.

Wife is a GP doctor, maybe 1/3rd of her patients have some form of this.

100% this. I've seen stats saying 20% of people in jail have untreated mental illness. I've spent a lot of time in jails and I would say it has be 80%+ because a lot of people can function enough to live in society and hide their symptoms until the point where they do something criminal.

Also (I'm hoping) the trauma of taking another person's life must be hugely upsetting. I'm hoping it's not something you do lightly, and is not without personal consequences (guilt,shame, shock,.. dunno).

Why would you hope that?

Can you really not think of anyone where it would be better if they were... not there anymore?