Make the enemy live up to their own book of rules. You can kill them with this. They can no more obey their own rules than the Christian church can live up to Christianity."
The left is never very good at using this tactic because their complete lack of understanding of religious or moral philosophy. It is Saul Alinsky's own rules of moral relativity and end justifies means that blinds the left to the full understanding of the right.
Actually this isn't an attack on Christianity. It's a rebuke of Christmas. It's a defense of Christianity:
2Ti 4:2 Preach the word; be instant in season, out of season; reprove, rebuke, exhort with all longsuffering and doctrine.
2Ti 4:3 For the time will come when they will not endure sound doctrine; but after their own lusts shall they heap to themselves teachers, having itching ears;
2Ti 4:4 And they shall turn away their ears from the truth, and shall be turned unto fables.
Santa Claus is a fable. Our society lusts after gifts. Our itching ears refuse the truth that our Lord created holy days and that they are inviolate.