Thanksgiving is the only major American holiday I have any respect for. It is everything Christmas was supposed to be. Remove the greed from Christmas, and you have Thanksgiving.
Thanksgiving is inherently religious. To give thanks is a transitive action, because there must be someone to whom you give thanks. Without that “whom”, it’s merely a day of reflecting on how much better your life is than others.
Therefore, atheists are not allowed to celebrate Thanksgiving. Neither are Jews or socialists. Sometimes they do anyway, and they rename the day to “Turkey Day”. Do not let them get away with this. Remind them that they are godless heathens bound for hell because they have no higher power to whom to give thanks. They already stole Christmas and Easter (and then always blame the Christians for Santa and the Easter Bunny when arguing religion with you, because athys have no self-awareness).
Thanksgiving is also inherently rightwing. It is about recognizing you have more than you deserve, whereas the leftwing is about demanding what you are owed. Thanksgiving is fundamentally a holiday about humility.