It's not Atheist complaining about having to take time off as opposed to those who hold another deity in a higher regard, they do not like to partake in the observance.
I am not religious but I have no problem with saying "Merry Christmas" and I don't place any emphasis that the words are necessarily structured to the birth of Jesus alone.
If people, who, like myself don't place and/or accept a necessary religious link could just stop and observe the beauty associated with Christmas, the lights, the smell of fresh pine, baked goods and good home cooked meals that bring family together the world could learn to, like myself, maneuver around those who do hold it as religious observance.