Do you know any adult that believes in Santa Claus? I mean not as an idea, but as a real living person who delivers toys to good boys and girls on Christmas eve. Of course you don't! We all grow out of that belief, even if we will always love and promote the idea of Santa. He stands for good and happy things and we need that in the world. But, Santa is a myth.
So why do people. otherwise intelligent adults still believe in "Jesus" and his amazing, mythical life and death? Yes, the idea of Jesus is a good one, the idea that some god came down and died to save us. But come on, we supposedly believe that he was "born of a virgin", which now we take to mean his mother never had sex...but the word virgin did not mean that at the time of the Bible. Virgin only means young woman, it has nothing to do with her sexual activities, only that she is young and female. We are supposed to believe that the birth of the "Christ Child" changed the world...how? Other than switching the titles of those in control, nothing much has changed. He was supposed to be the "Prince of Peace" and bring "good will to all men", but I see none of that in the world. If he is an all powerful God and was supposed to bring the world peace, he failed! There is no more (or less) peace on this planet now than before his reported birth. His death was also supposed to change things...again, no evidence of this exists. You can say "But I have a personal relationship with him and feel saved", well, good for you. But that is not proof of anything but your feelings/beliefs! At one time millions of people believed in Ra and the Egyptian Gods, that lasted for many more thousands of years than Christianity has but it is not proof of anything.
You may say that it is a unique and uplifting story that millions believe...again, not really. Everything found in the Christmas story and overall story of Jesus was done before. There are many son's of Gods or Gods who have supposedly been "born of a virgin", had come to earth to "save" everyone who believed in them. Many died and came back and overall, nothing is new or unique about the Jesus story.
Christianity is a mix of Jewish ideas, Greek and Roman Mythology and modern propaganda. I was a Christian for the vast majority of my life, I was a strong believer. I studied for the ministry and know much about what the Bible says and why. But in the end, I have come to understand that it is a Myth! The message of Jesus is a positive one (even if 90% of his so called followers don't actually do anything he said to do). But in the end, to believe in Jesus and the whole Christmas/Christian myth, is as unrealistic as still believing in Santa!