A big error has haunted humanity for centuries: it's the equivocation between generosity and altruism.
The former is a virtue any decent human being will practice: It asks of one to reach out to deserving others in times of dire need. The latter is a policy of devoting oneself to benefiting others above all. The former is admirable; the latter is suicidal.
Sadly, the two are often confused in the minds of many folks who have forgotten their college ethics courses in which these distinctions are usually discussed (when the professor isn't using the course to advance an agenda in support of the confusion!)
Aristotle knew that among the virtues human beings should practice one of them is generosity (or liberality). Of course, for him the others include honesty, liberality, prudence, magnanimity, courage, etc. Since Aristotle identified the purposes of practicing the virtues as human happiness – a virtue of a good-making attribute of a person and for persons the highest good is happiness – so clearly he was not championing altruism, which, as the philosopher W. G. Maclagan makes clear, amounts to "assuming a duty to relieve the distress and promote the happiness of our fellows…. Altruism is to … maintain quite simply that a man may and should discount altogether his own pleasure or happiness as such when he is deciding what course of action to pursue." ("Self and Others: A Defense of Altruism," Philosophical Quarterly 4 : 109-110.)
As presented, ordinarily by ministers, priests, philosophers or in fiction, altruism means ranking looking out for others first in one's list of moral duties. Because for much of our modern era prudence has been thought to be something we practice automatically – "everyone is selfish or self-interested" – the virtue has gone pretty much neglected. And since self-interested conduct was taken by many over the last four centuries to be innate, altruism is the doctrine that needed to be defended and practiced. As if people really did pursue their own best interest as a matter of an innate drive.
Yet, what is in one's self-interest – real self-interest, not just what one would prefer or like – is not simple to ascertain. It requires understanding oneself not only as a human being but as the particular individual who one is. What Plato said about this in the Phaedo (115b) is instructive:
"Crito, 'When you are gone, Socrates, how can we best act to please you?' Socrates: 'Just follow my old recipe, my friend: do yourselves concern yourselves with your own true self-interest; then you will oblige me, and mine and yourself too.'"
Indeed, in Classical Greek ethics doing the right thing is what's crucial, and that will be of benefit all around, helping oneself as well as others. But doing the right thing is something one must choose to do. It doesn't happen automatically. In how ethics is viewed by a great many thinkers today, whatever the right thing is will be done automatically – we are hardwired to do it. Doctrines are proposed in various fields – including the latest fashion, namely, neuroscience – as to how people and other living things are programmed by biological imperatives to serve others (or not). Never mind that ethics is actually about what people ought to choose to do, not about what they are impelled to do by their biological constitution.
Wouldn't it be advantageous if everyone instinctively did do what is right!? All would be just fine with the world then, at least as far as human affairs are concerned! But in fact, there is a lot of mischief going around and it is often due to bad choices people make. What would bad choices look like? The ancient Greeks had a good clue – ones that thwart or undermine our human happiness. Even generosity was, for them, a virtue that enhances the life of the one who practices it.
Those who peddle altruism, often so as to instill guilt in most of us who are quite normally seeking to benefit ourselves first and foremost, are in fact misanthropes, like the extreme environmentalists, some of whom – e.g., David M. Graber – actually hope for the extinction of the human race. (Another is the radical environmentalist Bill McKibben who prides himself on no longer being a consumer. Perhaps he would like to explain the virtue of this in our time to all the unemployed among us.)