Suicide is irrational! However, people that commit suicide are often psychologically unwell. One of the foremost researcher on suicide, Emile Durkheim, stated that suicidal thoughts could be as a result of poor social bond or restrictive social system whereby people believe suicide is better than living. The best way to help them is to form bonds with them, make them understand that they matter.
I certainly wouldn't encourage suicide, but I find what you said interesting. You declare that suicide is irrational. Irrational means "inconsistent with reason or logic" or "affected by loss of usual or normal mental clarity" (
https://www.thefreedictionary.com/irrational). It is impossible to imagine that somebody could use reasoning and make the decision to commit suicide with normal mental clarity? I think suicide usually happens when people think it is better to be dead than to continue living. Of course, most times this is done out of desperation, when people are not thinking clearly. I think though that it's possibly that somebody could decide to commit suicide in his/her right mind. This could especially be true in case where somebody is suffering from a terminal illness.