SFPW: The only time I "left the truth," was when I studied the JW teachings for a few years.
That said, I love this question!
I have many fond memories of Christmases gone by... Sadly, the days of our entire Family getting together for fodo and festivities, is now gone. The JW's have infiltrated and succeeded in dividing our family in such a way, that we no longer see our JW relatives.
The holidays have become a major point of contention, and the WTS has succeeded in their goal. Their true motive in abstaining from family celebrations, is to isolate and control the JW Followers. My young niece and nephew are now singled out of our family, not allowed to celebrate or receive gifts from us. This indoctrination serves more than one purpose.
as others have suggested, their separation from family gives them a feeling of being "different," "chosen," and most of all "superior" to the rest of us, who have succumb to the tradiations of gathering ourselves together. Eating and exchanging gifts, with some members traveling longer distance, to "come home for the holidays," is not displeasing to Jehovah God, our heavenly father. It is displeasing to his earthly organization. The GB wants to maintain absolute control and power over every day of the year. Do not forsake the kingdom work, just to spend even an afternoon with your unbelieving relatives!
Maybe you are asking this question, because you are considering a holiday celebration yourself. Do you have any relatives or people you love, who celebrate Christmas? there is likely to be at least one aspect you would enjoy. I especially like the singing and it is so much fun to go and sing carols to shut ins at nursing homes.