Happy random set of circumstances day?

I am back from Thanksgiving festivities, and wondering about something.

Why do we still celebrate Thanksgiving in the US? Isn't it a violation of the separation of church and state? After all, thankfulness requires two parties; the person giving thanks and the person being thanked.

I don't understand, therefore, how this can remain a federal holiday, given the fanaticism of the freedom from religion crowd.

I wonder how many years of it we have left...