While I think this is a reasonable sort of surface-level interpretation, I think it misses a bit of what typifies mental illness versus just being destructive, malicious, desperate, or extremely entitled.
Mental illness is something your brain is doing to you. It's not just a thought that you have and roll with, it's a persistent pattern that you struggle against. Just deciding that the thoughts and feelings being produced are inaccurate or unhelpful doesn't make it go away. It's not just extreme emotion, it's emotion that's being switched on in a way that isn't tied into the continuity of your more volitional patterns of thought and feeling. It's not just that the thoughts and behaviors playing out are unhealthy.
To put it into metaphor, think of your life and your interactions with the world like a video game, with your brain being essentially your character controller, interpreting your actions and bringing them into the world. You can decide to do healthy or unhealthy things with your character, but those things are under your own volition. Mental illness, then, is like a poorly coded character controller throwing errors and causing unforeseen bugs. Like, for example, if I push the down button there's a 30% chance that I randomly move to the left first, rather than moving in the appropriate direction.
That 30% chance might send me careening into a pit, but chances are that once I'm used to having this bug, I'll be aware enough of it to try to compensate. It might not always work, and I might drift a little left occasionally, but if I give myself a bit wider berth for any obstacles on my left, I'll probably be okay. This is distinct from someone who uses their volition to throw themselves into a pit on purpose.
Are both potentially bad for the character's health? Yes. But only one is caused by a character controller error, and because my goal isn't 'throw myself into pit', I'll probably do a much better job avoiding pits than someone who's jumping into them intentionally. These two problems are fundamentally different in that one is a product of a person's volition, while the other is a problem with the means by which they interact with the rest of the world.
That's not to say that people with mental illness are going to accidentally assassinate someone because they pressed down and went a bit left, but it illustrates the fundamental difference in making a bad decision versus struggling with errors in your brain.
That someone jumps into a pit on purpose does not imply that their character controller is bugged, especially if they smoothly beeline it while showing all signs of acting with intention.