As I have posted in this space before, "we"celebrate two separate holidays on December 25th, and unfortunately they both go by the same name: "Christmas."
One holiday is a secular one, dating back to Roman times, where we have decorated trees, gift-giving, a "jolly old elf" bringing gifts for the children, seasonal music, and so on. EVERYONE can celebrate that secular holiday, and the proof that it IS a secular holiday that government employees get paid not to work on that day.
The other holiday ("holy day") is a religious feast where Christians celebrate the Nativity - the supernatural virgin-birth of the God-man whom we refer to as "Jesus Christ." We symbolize this celebration with depictions of a baby laid in a manger in a stable or cave of some sort, and we say prayers and sing hymns celebrating this wondrous event and phenomenon. Only Christians celebrate this holiday/holy day. Christians who want to celebrate with gift-giving (should) do so on January 6th, the date when we celebrate the visitation of the three Magi (or "wise men") to the Christ child; they brought gifts of gold, frankincense, and myrrh.
But there is no good reason why everyone in the country should not celebrate a holiday on December 25th, and only a certified wanker would be offended by being wished a "Merry/Happy Christmas."