I don't know if it's true that you haven't affected the people in your past, but even if it is, that doesn't mean you won't affect people in the future. Depression is telling you that you can't do any more than you already are, but clearly you're a good writer and you think a lot and you really can affect people that way.

I don't like to talk about suicide as being acceptable or unacceptable, but let's say reasonable or unreasonable. I don't think it's reasonable to kill yourself because you think there's no hope for the future. You can't see the future, no matter how obvious it seems now.