Many churches have "Rally Day" or "Gathering Sunday" or such on the Sunday following Labor Day. That may include picnics or cookouts, etc. My friend's birthday falls on that date, anniversaries, etc. This year my DD starts a soccer program that day. Life goes on, but those kind of things are taking place unrelated to the historical events of that day. I don't understand the "celebration" in relation to the significance of the date, that doesn't sound right. I would attend another happy or celebratory event that day if it was unrelated to the tragedy, but I wouldn't want to attend any "celebration" that intentionally connects itself with 9-11.