Interesting little essay. I can't see any good arguments against it. We are all in a situation where we could save peoples lives if we only wanted to.
That's true, even if there are people who actively impoverish other people and killing people. They have a far more moral guilt and responsibility for the people that are killed and who live impoverished lives.
But, as we live in the real world, that doesn't change the fact that all the money we spend on tings that are not necessary to support our lives could be spent to save other peoples lives.
But, do we really have a moral responsibility for other people? I say no. Then the whole argument falls apart. I don't judge Bob for chosing not to divert the train from the child to his car. He's not actively responsible for the train killing the kid. And I feel as well that I'm not morally responsible for saving other people. I don't even have a moral responsibility for my family, except for my future kids, because they can't choose to be born.
It's not in human nature to be altruistic, but it's natural to care for one's family and friends because they are important for oneself.
Yes, we could all be saving peoples lives if we wanted to, but we are in no way obligated to do it.