It’s true that Thanksgiving was first observed by the Pilgrims (Puritans) and was institutionalized by a secular government. (Lincoln was brought up Baptist but never joined a church as an adult. FDR was brought up Episcopalian-Anglican.) Also (to my knowledge), the only other religion/culture/nation that had a gratitude festival before the USA were our Jewish predecessors.
But it’s also true that Canada adopted Thanksgiving because it seemed the right thing to do. So in a sense, that day is a witness, in its own unconventional way.
Almost everyone living in the USA observes Thanksgiving: atheists, Buddhists, Catholics, Dutch Reformed, Episcopalians, Flying Spaghetti Monsterists, Gnostics, Hindus, Incans, Jewish … through the alphabet to Zoarastrians, if there are any left. In the process, children who have to do homework about Thanksgiving learn a little about what it is, i.e. that people who were grateful to their Triune God wanted to show that gratitude.
So it seems strange to me that followers of Christ are the ones doing so much to undermine Thanksgiving. When I hear about “the war on Christmas,” I wonder if it’s already lost if there is no Thanksgiving before it.
Christians are to be thankful every day. This is true. But when I hear,
why does it have to be that day, I suggest that they could go shopping any day (so why does it have to be that day). There aren’t a lot of days left for people to spend time with their loved ones. And some day, you’re going to want to, and you won’t be able to.
Not-so-fun fact: I knew a divorced couple in which the custodial parent told the children,
Noncustodial Parent never has you for Christmas because NonCustodial doesn’t want to have you then. Non is the type of person who would rather wait until after Christmas and buy your presents for half-price. Lovely couple.
And yet because of spending time with them, I do more of my shopping in January than any other time of year. Black Friday or [winces] Black Thursday deals are cute compared to 90 percent off deals in January.
(True, you cannot purchase the hottest new toys in January, because they haven’t been invented yet. And you can’t purchase Christmas clothes in January because the person might not be the same size a year from now. But then, what child ever said,
"Wow, thanks! May I invite my friends to come over and play with my new clothes? 
I’d say, buy the kid clothes when they need them … but unless they teased a skunk I doubt they’d need new clothes this-instant-now on Thanksgiving day.)
