Not gonna lie, this confuses me a bit.
Mental illness spans a very large array of different ailments, and doesn't necessarily only mean personality disorders. I mean, just look at the DSM-5 and you'll see what I mean.
Normal people don't think about killing themselves. I'm pretty sure that's why they can't begin to understand why anyone who is suicidal is the way they are.
If you have any relevant journals that have cases of suicidal ideation in the absence of any physical or mental ailments, I would love to read it. Seriously, that would be fascinating.