What is wrong with being selfish?

 Can someone answer for me this simple question? What is wrong with being selfish? Like at all, why do we vilify it? Far as I am concerned, selfishness is a normal, natural part of the human experience. Humans can and should be concerned with themselves and not always altruistic. There needs to be a natural balance.  In all forms of media, any one that says they come first over others... is vilified and hated. I never got that. Altruism is not always the way, and it is time we recognized it...  People caring for themselves is healthy, and serving others is sometimes a bad thing if only personally. People wasting away and losing all they have, being labeled heroes for serving others. It makes me sad. We should really encourage kids, especially kids, to sometimes put themselves first...  Do you agree? What are your thoughts on this? I see it moving even into our stories, especially Young Adult novels where the main character is often a whipping post for everyone and never thinks of their own needs...  So... Yeah! P.S. I apologize if there are typos I missed, my software is being odd...