Gaon: You are simply, and completely, and absolutely incorrect about the *METZIUS* of Halloween, otherwise known as All Saints’ Day and All Hallows’ Day. It most certainly is an official Christian festival celebrated and consecrated TODAY by the Roman Catholic Church, the Anglican Communion, the Methodist Church, the Lutheran Church, and other Protestant churches. Christian celebration of All Saints’ Day and All Souls’ Day stems from a belief that there is a powerful spiritual bond between those in heaven (the “Church triumphant”), and the living (the “Church militant”). In Catholic theology, the day commemorates all those who have attained the beatific vision in Heaven.
Everything you said about the halachic status of Halloween applies equally to Christmas and vice versa. Christmas, too, is celebrated today in a mostly secular fashion, even by those who aren’t religious and aren’t Christian.
To paraphrase you, the fact is that Halloween is an official holiday directly associated with religion.