I don't think mental illness is really analogous to physical conditions in this context, because by their nature they interfere with concepts of free will mostly imagined by people who've never actually had to deal with that sort of issue.

I mean, I'm absolutely not saying that it's categorically impossible to unlawfully induce a vulnerable person to commit suicide, but I'm also pretty leery of breaking chain of causation so easily because in the absence of conditions like specific forms of brain damage or specific drugs there is still an adult human being involved in the process and it's is arguably insulting to a majority of people dealing with mental health issues to discount their own input as opposed to their diagnosis even in stressful situations.