Dear GoldStone and Jacob,
First and simply said, is you are right. Less than 5 out of six people have belief systems, and act on them. So to suspect that most people are not altruists is certainly a good thing.
To give (or become) the person your family needs to make the pieces work is a terrible burden for children. And when I did take on those burdens from 4 to 15, I thought I was excersizing my choices. What I have learned, for the first time, at 55 or 60 is I had so few alternatives, that I didn't really have a choice just equally bad options.
Being my mother's confidant, negotiating for expressions of my father's love to my mother, being abused by my older brother both physically and sexually (he was sick - suffered from gran mal siezures- we had to make allowances for him. Even having my mother decide that she remained in a the domestic violence for from 1946 to 1999 because of what I said when she was 39 (I was 9).
I think I know what you are talking about. We give all we have, and it is never enough. Consider Rabbi Hillel instead of St. Francis.
If I am not for myself, who will be?
If I am for myself alone, what am I?
If not now, When?
May you go with God (Or if you don't believe in God, go with plants - they give you oxygen. Maybe not for altruistic reasons, that is just what they do.)