Having an ego (I am using the word in the sense which means the part of you that goes
me) is natural. It tells you that you are important and it gives you a meaning (even though it may become very distorted) for your self-worth. It can act like a coping mechanism like it was mentioned earlier. It drives one to achieve, seek recognition, and to assert oneself. Selfishness is somewhat natural because its main drive is self-preservation and it can drive one to change one's surroundings to how you want it. So, it can help to discipline oneself instead of just sitting there and go along with the flow of others. The degree of how large one's ego depends but most people have some. Rarely, but there are people who have very little of it and they can be defined "selfless". They just do not desire much and can give themselves to others naturally. Perhaps, some become depressed because they have their self-worth wounded and their ego can not cope with it.
Personally, I think I am fairly selfish in nature. I have been even called childish and "immature" at times.
But some nature in one's personality, selfishness in this case, is something you can't change and something you have to live with.
Norsemaiden said:
It should have been mentioned by now but "pride" is one of the seven deadly sins! I doubt anyone here would agree with that idea.
Not just Christianity but the other major religion condemn it because its a tendency that those with large egos are disagreeable in nature. Firstly, they believe that ego can become so large to the point that it makes one insolent to God and order. So, they think need to be tamed to be able to make them obey their religion. Secondly, selfishness is equated with the very origin of evil because they think it can drive one to do anything to get ahead including exploiting others. Thirdly, it is believed to be a source of constant dissatisfaction instead of being content in their place. You brought up Nietzsche, and in his writing he constantly opposed traditional values of religion like humility, patience, compassion and so on and praised egoism as healthy.
One Buddhist commented that having a large ego makes one childish, angry, and their souls ugly. There are bad aspects of having a large ego and what he said has some truth. He categorizes people like that having souls which leads them to the path of Asura. In the Japanese Mahayana school of Buddhism, which he is from, there is the well known belief of 6 paths which are Deva, Human, Asura, Animal, Hungry Ghost, and Naraka. Asura was originally a god of justice but has later became the god of constant conflict. Those with Asura traits he explain to have a soul which is ruled by anger and it makes one overly self-interested, paranoid, envious, and hateful which all drives them to battle. It does not matter if you're not personally Buddhist or religious at all, but it is true that generally those with large egos to be quarrelsome and ready for battle. Possibly people with large egos strongly desire recognition because they have knots of insecurity and fears behind the surface.