What we need to be told is why this way of securing pleasure is especially meritorious. That is why their answers are unconvincing. I think not. With Machan, we can reject the demand that we set our own interests and projects on a par with those of all others. We are rationally entitled to lend to the one life we live our primary attention.
Primacy is one thing, though, and exclusivity quite another.
To count oneself as one and others as zero would be to fall into a kind of moral solipsism. The generous person is not solipsistic. He expresses his recognition of others' status as persons with ends of their own rather than mere things by forgoing from time to time his own satisfactions so that others can benefit. This isn't masochism or heroic self-sacrifice. It's no more and no less than generosity.