People aren't suicidal meerly because they are selfish, they are suicidal because they can't cope... Also, we all have different resources (both internal and external) to help us cope, and some have fewer than others... So just because one person can deal with a problem doesn't mean a different person can... Some of us are thrown over the edge more easily than others when faced with various stresses.
I work as a preschool teacher for at-risk kids... We seek out those who are abused, whose parents have drug/alcohol addictions or mental illnesses, who have parents who are in prison, who are living in extreme poverty, etc, etc... In that sense I devout my life to helping others. I am a vegetarian because I don't want to contribute to the suffering of other creatures... I avoid buying from companies that employ sweat shop labor (which unfortunately we can't entirely escape), I do my best to give my son a good life and lots of love... I DO care about others, but quite frankly, I suck at caring about (and for) myself. I go to bed every night wishing that I could kill myself, not so much because the world has failed me but because I lack the internal strength and capacity to deal with life, but I go on living because I don't want to hurt the people who love me.
I guess my point is, most people aren't going around saying that they want to kill themselves because they think death is such a great thing, they are saying it because their hope is already dead and they see it as the lesser of evils... As the one option that might actually reduce their suffering when everything else has failed. And while suicide its self might be a selfish act, it's really more about a depletion of resources for coping than it is about being selfish.
Also, I was first hit with major depression/suicidal thoughts at 16... I have had my ups and downs since then, but a decade later it's not truly better. Depression impacts people of all ages.