I wish all Happy Christmas.
Happy Christmas is different from Merry Christmas. Merry need not be happy and happy need not be merry.
Many people have holidays because of Christmas and it is appropriate that they wish Happy Christmas. Everybody is not a Christian. I know some Christian sects do not celebrate Christmas. People who do not celebrate Christmas are free not to accept or reciprocate the greeting. That does not mean that Christians who celebrate Christmas should wish Happy Holidays instead of Happy Christmas.
Last year I watched on Night Out on NDTV 24×7 greetings of many Hollywood actors and actresses. Most of them are Christians. Most of them said “Happy Holidays”. Some said “Merry Christmas”. Sylverster Stallone said “Merry Christmas and Happy Holidays”. Daniel Craig said “Happy Christmas”. I wish more people had said “Happy Christmas”.