I honestly can't come to a conclusion on this.
Yes & No are my answers. I know a parent that committed suicide...their children have struggled and been destroyed emotionally and mentally since. I find leaving them for one's on relief 100% selfish. However, I also find wanting someone suffering, to stay, a little selfish (no child understands that though...at all).
My personal belief, is that I'd never EVER abandon my children or loved ones due to my own suffering. I mean to much to them and love them. Having said that, I've never once, in any way, wanted to die. Not when my dad died, not when my ex-wife cheated multiple times, not during my divorce, not when I hurt my back, not in 2008 when we lost everything to the crash...etc.
My ex-wife wanted to die (tons of mental health issues) multiple times, and I could never understand/grasp it with our two beautiful daughters being there. Her suffering (all mental, we had a great life compared to most) was absolutely real to her though.
Edit* For some reason I read the OP as "selfish" rather than "cowards". In that case, the cowards that do it are the criminals/evil people that do it to get away from justice/being held accountable. I'd say it takes the opposite of a coward to go out by your own hand for anyone else.