[Sloth]

None is required. It's Christian because it is something Christians celebrate. The birth of the savior. The gift of salvation from God.

OK. But it's nothing that God has asked for. And it has certainly become a secular holiday, regardless of the origin, which is partly pagan, anyway.

"One person esteems one day above another; another esteems every day alike. Let each be fully convinced in his own mind. He who observes the day, observes it to the Lord; and he who does not observe the day, to the Lord he does not observe it." - Romans 14:5-6

[Protagoras]

OK. But it's nothing that God has asked for.

God asks for people to be happy and give thanks to him for gifts he has given. He didn't bother to pick a date, that is up to you. He did set aside one day a week, the sabbath. He actually asks that you do it continually, but particularly on the sabbath. Setting aside a special day to do so is perfectly legitimate.

And it has certainly become a secular holiday, regardless of the origin, which is partly pagan, anyway.

Non believers and pagans have co-opted a religious holiday, Christians have allowed it. They have recently been exerting their rights to express their opinion to these goofy people that they are tired of being insulted by the attempt to secularize a joyful religious holiday.