Why would you be mad at someone for enjoying and celebrating Christmas for family time? That's the most selfless interpretation of Christmas, in my opinion. A holiday is not a definition that is given to you, it's something you define yourself by your own experiences and feelings, as you are the one who is celebrating said holiday. Christmas was started due to religion, but it doesn't need to be religious to be celebrated. That's like when I'm in Honors Choir, and we have to sing songs involving the Lord in them. They were created out of religion by the composer, but I can interpret them in my own way, because I don't celebrated a religion, and create my own meaning to them to more deeply connect.