I think sharing holidays with family and friends is what it's really all about. I hate the thought of anyone being alone at the holidays so everyone who is willing to eat my cooking are more than welcome!
I say Christmas should be spent with those we're close to and whom we love. Some friends are just like family, so why would I want to exclude them? Sometimes friends do more for you than family.
I also happen to be someone who doesn't have family any closer than 9 hours away, so I can't always make it home to enjoy the holidays with family. Having good friends include me in their festivities is thoughtful and considerate. It is appreciated more than they know.
I also have a friend who is estranged from her siblings and whose parents are deceased. Does that mean she should spend the holidays alone? No, it means she's always welcome at our holiday celebrations, whether it's Christmas, Easter, New Year's or even July 4th. What are your thoughts?