Anyone still muddled over the actual nature of altruism would do well to read the man who coined the term.
Here, August Comte makes it completely clear that when he talks about the duty to sacrifice self for the sake of others, he really means it. It's also clear, even from this brief passage, that it is incompatible with liberty.
“[The] social point of view . . . cannot tolerate the notion of rights, for such notion rests on individualism. We are born under a load of obligations of every kind, to our predecessors, to our successors, to our contemporaries.
After our birth these obligations increase or accumulate, for it is some time before we can return any service. . . . Any human right is therefore as absurd as [it is] immoral.
This [to live for others], the definitive formula of human morality, gives a direct sanction exclusively to our instincts of benevolence, the common source of happiness and duty. [Man must serve] humanity, whose we are entirely.”
[Catéchisme Positivist, 1852]