Those who proposed the creation of Earth Day started out having it celebrated on the first day of spring (as if in mockery of and competition to traditional pagan spring celebrations). That its date has been rescheduled, as you note, to fall during the Judeo-Christian holiday season does make one wonder if the environmentalists aren't doing the same to Jewish and Christians. It could be said that environmentalists either can't be original in their calendar dating or are purposely trying to goad anyone with religious beliefs which contradict their political agenda (which wouldn't surprise me, since the environmentalist community so often behaves as a political cult).