Under God is in the pledge because that was what our country was built upon. Where do you think that our judicial system came from? Honestly think, where would we have gotten understanding of or basic rights and wrongs if it were not from the ten commandments?
The original pledge of allegiance never had the "Under God" part in it. That was added by President Eisenhower, along with the "In god we trust" printed on the bills. http://en.wikipedia.org/wiki/Pledge_of_Allegiance
Our country was founded on freedom of religion. One of the hugest reasons why we had 13 colonies was because people branched out all over the new world because they were being KILLED in certain places for wanting to practice a different religion. We were not founded on Christianity and in fact, that annoys me greatly because it seems that nobody knows history anymore. If you look into it almost all of the founding fathers were DIESTS or ATHEISTS. The man who wrote the Declaration of Independence, Thomas Jefferson himself, made many a quotes about atheism and how he didn't like religion.
And also, people were around before Jesus and where do you think they got their ideas of right and wrong then? As society grows, it becomes common sense to do certain things and we don't need 10 commandments on stones to tell us. As we evolved we would have learned killing our own people was detrimental, that stealing from ourselves was detrimental, that fighting with ourselves was detrimental. All these things that we supposedly learned from religion, are just things our brains learned for themselves as they involved. In fact, even most lion prides, and other animal species, don't harm one another (unless it's for self defense) because they know that killing their own is not good for their species. And I don't think that they have a religion or a God that they talk to. It's called natural instinct.