True or not, it doesn't matter for the purpose. If somebody is mentally ill, it doesn't matter what the cause is or who we can blame it on, it's still the case that cutting them 4 figure checks monthly is not going to magically get them out of their situation.
No, it's the reason the bad decisions get made. Same as alcoholism, drug addiction, and other "vices". Some may stem from initial poor decisions in the past, but they're all good contexts for why continued, daily bad decisions are made that serve to keep the person in poverty.
We ought to support NAMI (http://www.nami.org/). They're a large, slowly growing non-profit organization of doctors, families and researchers that is trying to get the US to shift the way it deals with mental illness from the bottom up: identification, treatment, support, public perception, everything.
Protip: This would also help with our mass shooting problem, too.
None of the things in that list were themselves decisions. They were causes of poor decisions. Do you dispute that mental illness can be a cause of poor decision making?
This is hardly a "decision somebody made".