This should be a no-brainer, right? Well for a significant number of Orthodox Jews, it’s not so obvious and that fact speaks volumes to the thinking of many in that community. Interestingly, it is precisely those who think the answer should be ‘no’ that are more accurate about the historical origins of the holiday, and I actually have great respect for that even if I totally disagree with the conclusion at which they arrive. But what really makes this question interesting, is that how one answers it, is a kind of Rorschach test which reveals how one thinks about Jews living in a largely non-Jewish culture.
The arguments against observing Thanksgiving are all based on Leviticus 18:3, which reads, “You shall not copy the practices of the land of Egypt where you dwelt, or of the land of Canaan to which I am taking you; nor shall you follow their laws.” Some halakhic (Jewish legal) authorities rule that observing Thanksgiving violates this rule while others do not. The issue which divides them is generally whether they see Thanksgiving as religious or not.
Those who embrace Thanksgiving, do so on the basis that it was “always a secular holiday”, to which anyone with even a rudimentary knowledge of history responds, “are you kidding?!”

To whom were the Pilgrims thankful? The whole story is one of deep faith and providence helping the Pilgrims persevere, build cooperative relationships with the native Indians, and create a new life in a new land. In fact, the idea of a secular Thanksgiving would have horrified those who first observed it.
Thanksgiving was, and remains for many including myself, a deeply if not particularistic, religious holiday. And therein lays its greatness. You don’t need to belong to any particular religious group, or even believe in God, to acknowledge the powers greater than yourself which have carried you through the past year and helped you to build your life in positive ways.
Of course, the idea that something can be deeply religious without being unique to the religious group which created it is what so many people miss in their permissive attitude to Thanksgiving. And if the basis of such permission is the willful erasure of the past, then such permission does more harm than good. It tells people that Thanksgiving is okay because it was never “theirs” anyway. Sadly, that approach is diametrically opposed to the narrative which is based upon people being able to share the wisdom and practice of communities not their own.
The real question is why the options are either to ignore the past as a way to build a shared future (the case with those who embrace the holiday) or acknowledge the past and use that acknowledgement to divide us from our neighbors (the case of those who think that Thanksgiving isn’t kosher). We have a third, and far healthier, option.
Let us acknowledge the deep religious roots of Thanksgiving, appreciate that many things which begin as religious migrate into the domain of the secular, and celebrate that in no country have more people from more diverse cultures ever gathered to celebrate both that which they share and the beauty of the many things which differentiate them from each other.
Thanksgiving is sacred to America and should be sacred to Jews who are among the primary beneficiaries of all that this nation has to offer. The reason Thanksgiving should be celebrated is not because we lie about its past, but because in no way is America for Jews, what either Egypt of Canaan ever were. In fact, if there could be a promised land outside the land of Israel, this would be it. No America is not perfect, but the story of those who preceded us in coming here for their own religious freedom and opportunity is surely worthy of celebration. The story is theirs and it’s ours.