Of course atheists have faith. Just suggest that they either decline to celebrate Thanksgiving or rebrand it as “Plumb Dumb Lucky Day” to fit their belief in random, disconnected events. I did this in a blog a few years ago. The atheists were outraged because they were “thankful” for all sorts of things. But when asked where they directed their “thanks”, they became unglued. Atheists need the argument because they are the insecure side. They know they are wrong, but can’t admit it.
Speaking as an atheist, while I do "celebrate" Thanksgiving with my family, I don't actually give thanks to anyone, other than those who provide the meal (usually my sister and brother-in-law, these days).
I don’t “celebrate” Thanksgiving. It’s just a day off, with food, and football, really bad football usually. And nice weather, because I live in the desert and late November is usually an excellent time for bike rides, swimming, and eating on the patio. If I express any thanks to anybody it’s my wife and friends for making my laps on this rock more enjoyable.