How come Atheists and Christians can't get along?

This is most likely because Christians believe that the only possible explanation for the creation of the universe and our wonderful bodies as lives that we have as human beings is some supreme being that was in the shape of a human being who claimed to be the son of god, and god the father. Christians believe if you don't recognize this, and especially don't believe in God, you aren't admiring the creator of the universe and you don't value and appreciate human life. The truth is that many Atheists do appreciate human life, except they have different ideas about how the universe was created. They believe it always existed. I hope this helped.