Does it benefit a mother to sacrifice her life for her child? Who decides that? The mother does.
She doesn't, though, not by the measures with which the terms "altruism", "self-sacrifice", "self-interest", and damn near everything else in this argument are defined by general society, and indeed everyone in this thread other than you. The entire notion of self-sacrifice is that you have some real physical resource, even if it's some portion of bodily integrity, and by losing that without personally benefiting from the act, you demonstrate virtuous behavior because you place some other thing above your own
material benefits.
Fundamentally, the line of discussion is about
resources, not
feelings. Not preferences, not beliefs, the things being sacrificed are what you can hold, what you can touch, what is there for others to interact with. Because cognitive states cannot be determined definitively. Performative virtue is such a basic element of society that setting the bar at material detriment is a commonplace matter specifically because it weeds out the mere socialites who will sell themselves out the next moment in a wholly contradictory fashion, because they'll hardly ever surrender their physical comforts.
You seem to be trying to make a "ring -1" argument, trying to argue
below any actually observed phenomenon to argue
true motivations and pure reason... Without being able to understand the lines between interest as preference, interest as presence within a structure, and indeed interest as return on loan investments.
Also, generally, people behave in ways that can often be described by the social construct of altruism on an individual or tribalistic level, and very rarely on the species level.
The terminology used is "others of its species", not "the rest of its species", it's entirely applicable to benefiting only a single other individual. You're being a staggeringly
bad pedant who appears willingly ignorant of definitions, and you seem to hold the bizarre position that personal preference is the
only determinant of benefit. Not, you know, access to physically necessary resources. Or basic bodily integrity.
And the point of that is that altruism is not a social construct to begin with, it's a pattern of behavior that exists within purely instinctive layers such as the rudimentary responses of insects and pre-learning human actions. An infant's cries are no social construct, and the parent's response is little impacted by any such thing; both of these are wired into our brains at birth.
You are not the arbiter of what "altruism" means, and you keep demonstrating you take an utterly bizarre position on every involved concept.
No, but it being your preference as to what occurs does.
Fundamentally, preferences are what you
believe will make you feel good, they're even less objectively real than the emotions are! Just because "your preference" is to burn six figures of your own property, does not mean you have not been self-sacrificing, because you have made your personal conditions
factually materially worse for
no personal gains.