As an example, let's say that a guy has decided that becoming a successful computer programmer is what is best for himself. This means that will do things to help himself become a successful programmer. However, one night he decides to go out to a show and hang out with his friends. Now that time could have been spent studying or working on projects, but, alas, he did not. It may seem like no big deal, but if ethical egoism is true, then by going out with his friends (not what is best for himself) instead of studying (what is best for himself) he was acting immorally.
Weird, huh? If ethical egoism is true then you are being immoral if you do not do things that are the best for yourself. This theory locks you into what you have decided as the 'best'. If our programmer friend decides to change what he believes is best for him, like becoming an artist, then the whole previous time of his life has now been wasted and thus immoral.
Believe it or not, some can think there are a few reasons why ethical egoism is appealing. One is that it would explain why we would want to be moral. After all, being moral means doing what is in your best interests! Hooray! Another reason could be that it respects and values the individual. This means that what YOU think matters most. You being who-you-are is important, otherwise a universal truth (such as lying is wrong) that applies to all people would reduce your individuality. So by elevating yourself, you automatically become important. Another hooray!
Maybe you can already see some problems with this weird theory. Sometimes our own best interest is not served by ethical egoism! Here's an example that my teacher used to illustrate that point.
Suppose that you are in a class with 40 people. Each person is given a piece of paper with a red square and a green square. The rules are (1) Everybody must check one square and hand it in. (2) If everybody checks red, each person gets $1. (3) If one or more people pick green then they will split $10 and the people who picked red will get nothing.
Supposing that ethical egoism is true, what is in your best interests? Remember you MUST act in YOUR best interests. It took the class a little while to figure this out, but picking green would be in your best interest in every way possible. If everybody picks red but you, you get $10. If everybody picks red but you and someone else, you get $5. The more people who pick green means the less money you get since all of the greens are splitting the $10.
Have you figured out that if EVERYBODY picks green, then all you would get is a measly twenty-five cents? Wouldn't the common sense thing to do be to talk to all of the other classmates and all agree to pick red? Then everybody would be sure to at least get $1. Remember, though, if ethical egoism is true then you can't be concerned with other people and what's best for them. If you pick green you are guaranteed some amount of money. If you pick red then you aren't being an ethical egoist.
Also, if it really is in your best interests to all work together for a guaranteed dollar, then ethical egoism cancels itself out. In the case of the green/red squares, ethical egoism's advice (always act in your best interests) would be to not follow ethical egoism's advice and work for the common good instead.
Another problem is that ethical egoism violates ideas about rights, justice, and dignity. Something like theft could technically become moral if it is in someone's best interests.
So the concept of ethical egoism is rather silly. True, it's not a bad thing to sometimes work in your best interests. After all, it is in my best interest to eat food. It is in my best interest to have a job so that I can have money to pay for food.
People can have many interests but who is to say which are 'best' in any given situation? Here is something that Paul wrote to the Galatians. Do you see any room for anything remotely similar to egoism in this list?
"But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control" (Galatians 5:22).
I didn't think so. Furthermore, he contrasts the fruits of the spirit to those of the sinful nature.
"The acts of the sinful nature are obvious: sexual immorality, impurity and debauchery; idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions and envy; drunkenness, orgies, and the like. I warn you, as I did before, that those who live like this will not inherit the kingdom of God." (Galatians 5:19-21)
Finally, and most importantly, how are we able to have the fruits of the spirit? Certainly not of our own doing.
"Those who belong to Christ Jesus have crucified the sinful nature with its passions and desires. Since we live by the Spirit, let us keep in step with the Spirit. Let us not become conceited, provoking and envying each other" (Galatians 5:24-26).
Coming right out of the season of lent, we can see that Christ most certainly did NOT behave as an ethical egoist. I'm pretty sure that means we shouldn't either. :)
Thanks for reading!