Is there a difference between self-interest and egosim? Is there a difference between benevolence and altruism? The question is often framed as egoism vs. altruism, but this may be a false dychotomy.
I think that there is a sharp distinction between egoism and self-interest. I understand self-interest in the Lockean and Spencerian sense that it spawns social cooperation; that it is in our self-interest to interact with others voluntarily. So self-interest is good, while absolute egoism is a denial of all morality really. Egoism, in the Max Stirner sense, is "I can do whatever I want to anyone". Self-interest is quite different from that. In "Social Statics", Herbert Spencer pointed out that we regaurd the rights of others in proportion to our regaurd for our own rights; I.E. our self-interest.
I also make a distinction between altruism and benevolence. I see benevolence as being genuine goodness to others that arises out of self-interest, while altruism is the complete denial of self-interest and an embrace of a philosophy of absolute self-sacrifice either to a "collective" (that's the way that the term "humanity" or "society" is typically used by altruists) or to an oligarchy (and it's always oligarchic in practise). In this sense I'm an adherant of Ayn Rand's ideas; however I don't think that she adequately explained the difference between self-interest and egoism. She gives the reader the impression that she's an absolute egoist.
I understand the meaning of charity as voluntary benevolence towards others that arises out of the self-interest of the giver. The person who gives actually values what they are giving to; they find virtue in the recipient person or cause. Altruism, on the other hand, cannot be considered charity at all, because it is a philosophy of absolute self-sacrfice, I.E. servitude to the altar of collectives. While charity and benevolence is voluntary and genuine empathy or sympathy, altruism is coercive and fake empathy or sympathy. It's an erroneous view of positive obligations.
I understand egoism as being a form of hedonism. The egoist does whatever they like to others irrespective of both their own self-interest and that of others. To the egoist, might makes right, while at the same time they may try to deny the existance of rights. There is only power and one-sided utility to the egoist. In a sense, an egoist is a radical existentialist. All that matters is the present moment. Future consequences becomes irrelevant, as do all externalities from the egoist themself. The egoist lacks an understanding of what actually is in their self-interest.
There is a big difference between Adam Smith's "invisible hand", by which people cooperate and interact with eachother in each of their own self-interest to produce more good than they could have isolated by themselves, and an egoistic scenario in which people isolate from eachother completely because they refuse to persue their self-interest in a way that coincides with that of others. If everyone was an egoist, the human race would die off rather quickly, because there would be no real social cooperation. Instead, there would be social isolation, in which everyone tries to generalize in doing absolutely everything completely by themselves.
Unfortunately, this type of picture, of the isolated egoist, is commonly associated with the term self-interest to many people. But it is an entirely different thing. The "rugged individualist" has been mischaracterized in the popular mind of being an egoist. There is a failure to understand that self-interested individuals are capable of acts of benevolence, and that various acts of morality are indeed in one's self-interest. There is a failure to understand that self-protection is a necessary consequence of self-interest in an imperfect world, where things can go wrong.
On the other hand, most people's conception of charity and benevolence is altruistic and collectivistic. They are willing to support what is blatantly not in people's self-interest in the name of egalitarianism. Charity is seen as a positive obligation to be forced onto everyone, where each person has a positive obligation to do certain things for everyone else, completely indiscriminately, even if it is radically against the self-interest of everyone. There is a failure to understand that true kindness, cooperation and productivity is voluntary, not coerced at the point of a gun.