What it comes down to is that self-interest is part of human nature, altruism is not.
Altruism is learned, voluntary, and often (but not always) counter to self-interest.
Capitalism takes into account that human nature is involved (self-interest) and it prospers.
Socialism (at least the “benevolent kind that run-of-the-mill Useful Idiots subscribe to) erroneously regards altruism as a component of human nature, and it predictably fails.
Self-interest is not the same as selfishness, and therefore should not be regarded as a negative or a vice.
Likewise, altruism is not always the same as generosity, and is not always a positive or constructive trait.
Naturally, the class argued. We'd been raised to believe in altruism as being a selfless sort of thing, but eventually I reluctantly had to agree with him.
While it might not be as obvious, altruism comes with a reward for the altruistic as well as for the one benefiting from the act of altruism, so altruism is not really a selfless thing at all, just less obviously self-benefiting than the usual self-centeredness we run with.
In all these years since high school, I've yet to come up with an example altruism that doesn't come with some sort of reward, or isn't in some way benefiting, for the one being altruistic.
He was a good teacher and it was an interesting class.
Ayn, how’ve you been? You seem to have left out the concept of virtue.