I dunno if I like jumping to mental illness as an explanation for this in reinforcing established and disproven stereotypes
There’s always some mental health issues with something like this. The very concept of killing someone and knowing you’re going to die as a result requires an altered mental state.
I wouldn’t say so in every situation. I’m sure plenty parents would say they would die to defend their kid, and I don’t think that would quality for an altered mental state.
I mostly do agree though, but I do think you can sacrifice yourself as a rational and mentally healthy person. But it certainly not a choice that hypothetical person would make lightly.