I find it hard to believe that there is any reason good enough to do such a thing. Maybe people do it because they don't feel like they are part of something, or that they have let people down and things would be better if they weren't there for others to deal with.
Couldn't tell ya, haven't every really had the urge. Would've been way too chicken Shyt to even think about it.
I do though agree with death for me if it were to save someone else's life. Would gladly do it, given no other way out. I'm just not so sure you'd call it suicide. There would have to be someone giving you that choice.. you or another.. basically homicide right?