One can understand something even without approving of it. Empathy is a wonderful thing. I can even understand how some parents end up shaking their babies. It's wrong, they shouldn't do it, but I can follow the progression and see how they end up there.
Regardless of your intent which I assume is good, what you propose and the words you use are shaming to anyone who has ever attempted suicide or considered it. So they would have a negative effect.
Imagine this horrible scenario. Someone has stressed to their child that suicide is selfish, but through depression or some other series of life events they find themselves on the metaphorical precipice. Because they know that their parent disapproves, that they consider suicide to be selfish, that child may feel unable to talk to their parent. And yet talking to their parent is what might save them. Having someone listen without judging is more valuable than anything else to someone in that state of mind.
It's not a coincidence that suicides are more common amongst middle aged white males than any other group. These are the people who have been taught to be strong, not to cry and to stifle their emotions.
Don't take my word for it. Do the research, follow the link in the post above. Before you go doing unintentional harm learn about the subject.