Saint Nicholas was very real however, and had a mean right hook for heretics.

Of course, that's disputed. I tend to believe it, however, because the sources which relate the story also add the Nicolas was put in jail for it until he apologized for letting his zeal overcome him. It's not the sort of detail that fabricated accounts would be likely to include, but it's certainly what would have happened had Nicolas gotten a little slappy with Arius.

Didn't he drop bags of money down the chimneys of poor people? According to Catholic theology, Saint Nicholas as a saint can also bestow gifts via prayer, i.e. "prayers of a righteous man availeth much." So one could argue the essentials of Santa Claus are true in Saint Nicholas, and parents are not lying when they tell their kid that Santa Claus exists.

Sure, but they're teaching sacrilege to their kids.

Of course, but sacrilege is in the eye of the beholder. It used to be sacrilege to own a Bible not written in Latin and for a layperson to read it directly, now many Christians consider any Bible other than the King James version to be sacrilegious. There's no objectivity or rational thought at work, it's essentially cultural norms and politics.

Many Conservative Christians do believe Santa Claus is an attempt by the "atheist establishment" to remove the Christian identity from the holiday, but that's due to a modern interpretation of Santa Claus as a capitalist icon, and the defensive nature of Christian conservatism. No Christian would likely have questioned the "Christianness" of Santa Claus a century ago, when the status of religion in Western society was unquestioned.

Are there any statistics on what portion of parents actually tell their children that Santa is real? I was raised in the Midwest US in the 90s, in a conservative Christian family, and as far as I can remember I never thought Santa was real. My parents confirm that they talked about Santa and wrote “from Santa” on some Christmas gifts, but they never intended us to believe Santa was real.

I also don’t remember belief in Santa to be common among my friends. I remember one friend who expressed belief in Santa as a supernatural being, and everyone poked fun at him for it.

And that's why I will never tell my kids he is real.