First, let there be a distinction made between suicidal intentions and altruism—simplifying this by overlooking our inevitable various degrees of ignorance as concerns forethought. The person who jumps on a grenade because he’s sick of life is not the person who cares for his fellows and innately senses her/his duty to safeguard. And of course, there are vastly less extreme examples of unwittingly reciprocal altruism; give a child a present it cherishes and the child will later on in life hold warmer feeling toward you and those like you than otherwise. That said, giving a child a present with this reason consciously intended is, to my mind, a bit sociopathic; nevertheless, the pleasure one receives from so doing (to not address less common instances such as giving a few bucks to a homeless person on the streets) is one of assisting others with a sense of self-esteem or empathetic pleasure as reward—a satisfaction that serves a utilitarian purpose of reciprocity, even if in only the most abstract of ways.
The just mentioned can obviously be argued against—and once one accepts that altruism is real in a good number of people, explaining it is riddled with complications.
Still, to address the proposition that there is no true altruism on account of selfishness: To the persons who feel anything from a) lack of remorse otherwise present in not fulfilling an innately sensed duty to b) a sense of eudemonia in benefiting others, their actions will of course be out of self-interest and, loosely worded, thereby selfish. But their self-pivoting interests (whose intentions would they be otherwise) are those that strive for and become emotively rewarded by closer proximity to an ideal state of selflessness—at least in respect to those one cares for. There are of course those who take advantage of this, those who do not share the same goal of selflessness as their own self-interest. Sadly, a joyful coward will live to reproduce whereas a firefighter that dies in the burning building will not. Nevertheless, altruism—however further debated to be—can only be a behavior engaged in due to the intrinsic values held whereby others are deemed to hold their own intrinsic value, rather than merely holding instrumental value to oneself, here a type of value that is thereby disposable when no longer of use.
So the upheld fact that we are all selfish, with which I technically agree, does not then do away with altruism being at times a real aspect of humans.
Some species of animal, btw, are far more altruistic on average than humanity when addressed as a total species. Meerkats serve as one good example. They too behave thus out of their own self-interests.
My own perspective is that if we learn from the time we’re young that the only way to obtain satisfaction is by taking without giving and by domination (rewarded temper tantrums and the like), then we will likely behave in such ways as adults. But if we learn from our most important education—that of our social surroundings during our preadolescent years—the joys of sharing, of fairness, or compassion, and the like—even if we only acquire a taste of this joy—then we’re far more likely to be altruistic-leaning as adults, maybe most especially in times of need as regards those we care for.
Either way, we’re being selfish in seeking to obtain that which we cherish and value.
You yourself exhibit concern for the issue of humanity. Selfish as this concern might be, it is yet a concern that intends toward the wellbeing of others and, hence, is altruism leaning.
To decry that the altruism involved is not perfect misses the point of true instances of altruism. No one, for example, has ever experienced a perfectly true love in whatever form one wants to contemplate the term, yet there are instances of non-deceptive love all the time.
We can either foster these self-centered interests toward selflessness in ourselves and in others or, else, not foster them and instead seek purely egotistic interests. Can’t think of any other way in which there might be an altruistic future for humanity than by engaging as best we can in the first alternative in a fair and just way.
As far as our species goes, the future is contingent on our present actions.