I don't think selfishness comes naturally. I believe it develops over time through socialization and, in all honesty, it doesn't make you a good person just because you donate to a charity (looking at you stuck up rich people). Similarly, it doesn't make you a bad person just because you passed up a volunteer opportunity (more of a note for myself).
The reality is that to be truly happy, you need to put "you" first sometimes. If that means being selfish, do so with a smile on your face. Am I saying to ignore others or how they feel, always choose yourself or become completely inconsiderate 100-percent of the time? Absolutely not -- life is about balance.
Loving our children fiercely neither grants us a free pass to act as if we are the only people who adore our children nor does it give us a "get out of jail free" card to abuse teachers, coaches and other parents. Principles like fairness and respect still apply to us, even when we love our children so much we can scarcely see straight.