But that's a separate problem. Figuring out how to prevent mental illness is obviously important, but figuring out how to help cure it when it does happen is important, too.
Suicidal ideation is by definition not healthy. You can argue the ethics of suicide (particularly assisted suicide, which I'm opposed to), but there is no situation where it's a good outcome. It can only ever be seen as the least worst outcome, and if we ever change our collective opinions on that I think we are far down a dark path to great evil.
There's a huge difference between considering suicide if you're terminally ill and in a lot of pain, vs. considering suicide because your life is not going well and you're really depressed, which is something that may be treatable, and I expect the vast majority of suicides are the latter and not the former. I personally know one such example.
As someone whose life has been affected by suicide, and almost affected much more seriously by a close call, I see suicide as the ultimate failure, and think we should be doing everything we can to help people escape from these ideas (and yes, I've done hard work to help someone who had these problems, and that person is definitely doing better, and enriching his own life and the lives of others because of it).
Our world is making us crazy and sick more than it should, so attack the problem at both ends. Figure out the causes and the cures and try to stop the first and accomplish the second.