Since we each know what we want better than anyone else, we should pursue these needs – if we pretend instead that we should all be responsible for each other, then we’ll probably not fulfill our needs as effectively.
There’s the idea that we should “mind our own business”, which is a popular idea throughout history.
Taking care of someone else is degrading to that person because it assumes he/she can’t take care of him/herself. Finally, the idea of being ethical with other people is really self-interested anyway – because we want good treatment from others.