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.
No, you're wrong, this is an attack on Christianity and the way that we observe Christmas. Christmas, like many religious rites that do not derrive directly from admonition of Jesus, were made part of the early church worship service in an effort to make Christianity come alive for the many illiterate worshipers. The celebration of Christmas simply gives a special time of year for Christians to remember and celebrate the birth of Christ as told in the New Testament. What's wrong with that?