The first argument of the theory is about our only motives that people always and perpetually act to fulfill their own self-interest and these motives become selfish by its purpose or objectives. If this is true, then how do we explain the good deeds by other people? What about the heroes who fought during the revolution? Do you honestly think that saving their motherland was for their own interest? If psychological egoism really holds true, then can we say that this heroic deed is an act of selfishness? I guess not. This alone defies the concept of psychological egoism.
We have to realize that sometimes people do not act in accordance with their own interests. The second argument for psychological egoism that getting what one wants and receiving pleasure is also flawed based on the fact that all our successful actions are accompanied by pleasure (for us), it does not follow that the objective of these acts is pleasure for oneself. Besides, self interest isnt automatically discordant to interest in the welfare of others. A person may be simultaneously concerned of his own interest and at the same time the welfare of other people.
For example, a store owner doesnt swindle on his buyers simply because he knows honesty is good for business. Another for psychological egoism (pleasure, pain and moral education) is that the way to get happiness is to forget about it and psychological egoists/hedonists can not recognize this. Put in a simpler way, psychological egoism is flawed because in reality, people can be motivated not only by self-interests but by other factors from desire to hatred. In most cases, you feel good not because of what you did but rather from the fact that you know its good.
You do not help the needy because you know youre going to feel good after you have helped the person but rather because the act itself is good and morally fulfilling. In an essay by Brandi Davison, he established the strong and weak versions of ethical egoism. The strong version asserts that it is always moral to endorse your own good and it is never moral not to do so while the weak version says that even though it is always moral to endorse your own good the converse is not necessarily accurate (Davison, 2006).
Instances will arise where it is more important to disregard your own welfare when making a moral judgment. On the facade, the two may seem similar but are actually quite different. While both types of egoism discuss ones own self-interest, they are different in the sense that ethical egoism emphasizes that an individuals own welfare is the only thing that essentially matters for him and should seek as an end only his own welfare. It does not necessitate one from considering the well-being of other people in moral forethought.
It is not an imperative either that others also seek their own self-interest, just as long as you ought to seek your own self-interest. In other words, ones search for self-interest is indifferent of other people. Psychological egoism on the other hand, asserts that a persons deliberate action is the determining motive for ones own welfare. The motivation for each theory differs because unlike psychological egoists whose ulterior motive is selfishness, ethical egoism is driven by doing what is right.
The distinction between the psychological and ethical egoism lies in the contrast between is and should, fact and value and descriptive and prescriptive. So what then is the difference between self-interest and selfishness? Both concepts tackle the issue of self-interest. It is but important that we delineate selfishness with self-interest as there is a borderline between the two. Self-interest does not necessarily equate to selfishness.
Let me describe the difference between the two using a school setting. Self-interest is exemplified when a student plans ahead a step by step objective to achieve his goals. Selfishness are sycophants. The sycophantic student is a selfish student that tries to make themselves look good at the professors and other peoples expense. Therefore, selfishness is doing things entirely for your own satisfaction while self-interest is doing or acting what is to your best advantage in order to succeed.