Not all rational ability is removed by mental illness in every case
No, but I think it's ok to accept for many it does?
I'm very sorry about your father, and I'm sorry that as an adult you still feel it's difficult to deal with, and your view his act was selfish, is what matters, because you were his child.
But it's not ok to generalise, I'm sorry. Everyone is different. Suicide is not an easy option for anyone. It's one done by someone in a lot of pain, incapable of rationalising their act, in many and most instances. And maybe you can accept that although you do not feel this was the case with your father, that maybe for others, that is exactly the case.
Suicide by it's very definition will always be selfish. The question is deliberately selfish or not. For your father you feel yes, for others this will not be the case.
Kate spade took her life in such a horrific and brutal way I cannot even begin to comprehend how she must have been feeling, the pain she must have been in to contemplate it, never mind do it . I would suspect that was due to a lot of pain and an inability to rationalise her act.
I only hope her daughter can understand she was ill and this was a symptom of that, she very likely died due to mental illness, and I think that should be considered in many cases.
As a Pp said, it's easy for us to understand when our bodies are broken. It's not so easy when it's our minds. 💐