As for Satanism, etc, there is the famous quote from Eliphas Levi:
… we come now to the most atrocious mysteries of the Grimoire, those which are concerned with evocations of devils and pacts with hell. After attributing a real existence to the absolute negation of goodness, after hrving enthroned the absurd and created a god of falsehood, it remained for human folly to invoke the impossible idol, and this maniacs have done. We were informed lately that the most reverend Father Ventura, formerly Superior of the Theatines, Bishops' Examiner, etc., after reading our "Doctrine", declared that the Kabalah was in his opinion an invention of the devil and that the Star of Solomon was another diabolical device to persuade the world that Satan was the same as God. Observe what is taught eriously by those who are masters in Israel! The ideal of nothingness and night inventing a sublime philosophy which is the universal basis of faith and the keystone of all temples! The demon setting his signature by the side of God's! My venerable masters in theology, you are greater sorcerers than you or others are aware, and He Who said: "The devil is a liar like his father," would have had some observations to make on the decisions of your reverences.
Evokers of the devil must before all things belong to a religion which admits a creative devil, who is also rival of God. To invoke a power, we must believe in it. Given such firm faith in the religion of the devil, we must proceed as follows to enter into correspondence with this pseudo-Deity:
MAGICAL AXIOM
Within the circle of its action, every word creates that which it affirms.
DIRECT CONSEQUENCE
He who affirms the devil creates or makes the devil.
-- Le Ritual le Haute Magie, Chapter XV, Sabbath of the Sorcerers

Levi had a great influence on Crowley (who claimed to be Levi’s reincarnation). “ Left-hand path” has been used by those who may or may not be familiar with the writings Crowley but know he made use of the term. In their ignorance they claim all sorts of absurd doctrine and, not knowing what Crowley actually wrote or, more likely, simply hijacking the term, present their error as Crowley’s position on the subject. So much so that now the Left-hand path is commonly associated with “Satanism”. This is, of course, absurd. Crowley himself has this to say on the subject of the Devil:
Before leaving the subject of Black Magic, one may touch lightly on the question of Pacts with the Devil. The Devil does not exist. It is a false name invented by the Black Brothers to imply a Unity in their ignorant muddle of dispersions. A devil who had unity would be a God "The Devil" is, historically, the God of any people that one personally dislikes. This has led to so much confusion of thought that THE BEAST 666 has preferred to let names stand as they are, and to proclaim simply that AIWAZ --- the solar-phallic-hermetic "Lucifer" is His own Holy Guardian Angel, and "The Devil" SATAN or HADIT of our particular unit of the Starry Universe. This serpent, SATAN, is not the enemy of Man, but He who made Gods of our race, knowing Good and Evil; He bade "Know Thyself!" and taught Initiation. He is "the Devil" of the Book of Thoth, and His emblem is BAPHOMET, the Androgyne who is the hieroglyph of arcane perfection. The number of His Atu is XV, which is Yod He, the Monogram of the Eternal, the Father one with the Mother, the Virgin Seed one with allcontaining Space. He is therefore Life, and Love. But moreover his letter is Ayin, the Eye; he is Light, and his Zodiacal image is Capricornus, that leaping goat whose attribute is Liberty.
-- Crowley, Magick in Theory and Practice, CHAPTER XXI OF BLACK MAGIC OF THE MAIN TYPES OF THE OPERATIONS OF MAGICK ART AND OF THE POWERS OF THE SPHINX.

I have reproduced more of the section from Magick in order to demonstrate Crowley’s thinking on the subject. Note, foremost; The Devil does not exist. It is a false name invented by the Black Brothers to imply a Unity in their ignorant muddle of dispersions. A devil who had unity would be a God. Crowley covers the entire subject in three short sentences. Compare this to Levi’s assertion per the objective existence of the Devil. Next, Crowley asserts that the Devil is a concoction of the Black Brothers, though his meaning is not clear as to why. The “ignorant muddle of dispersions” that the Black Brothers are guilty of is, as we shall see, a reference to Choronzon, the Demon of the Great Outer Abyss. The Black Brothers have
(made) themselves a false crown of the Horror of the Abyss; they set the Dispersion of Choronzon upon their brows; they clothe themselves in the poisoned robes of Form; they shut themselves up; and when the force that made them what they are is exhausted, their strong towers fall, they become the Eaters of Dung in the Day of Be-with-us, and their shreds, strewn in the Abyss, are lost.
These are the Black Brothers who
are the Brothers of the Left Hand Path. These are they
who "shut themselves up", who refuse their blood to the
Cup, who have trampled Love in the Race for self aggrandizement.
-- Crowley, ibid.

In the Vision and the Voice Crowley given the interpretation of this Arcanum
But they that are without understanding have interpreted all this askew, because of the Mystery of the Abyss, for there is no Path from Binah unto Chesed; and therefore the course of the Flaming Sword was no more a current, but a spark. And when the Stooping Dragon raised his head unto Dath in the course of that spark, there was, as it were, an explosion, and his head was blasted. And the ashes thereof were dispersed throughout the whole of the 10th Aethyr. And for this, all knowledge is piecemeal, and it is of no value unless it be co-ordinated by Understanding. -- Crowley, Liber 418: The Vision and the Voice

Note that “They who are without understanding” are the Black Brothers. Crowley here claims that knowledge (Daath is referred to as knowledge) cannot ever be whole as knowledge is fragmentary below he abyss. Therefore, the Black Brothers have taken an illusion (the universe) and
They make themselves a false crown of the Horror of the Abyss; they set the Dispersion of Choronzon upon their brows (Liber 418, ibid.)

To summarize, the concept of the Devil as an anti-god is an error that has been perpetuated from the Middle Ages to now, having reared its head in the Witch hunts and pogroms of the period rightly called the Dark Ages. In the current atmosphere of Apocalypticism, the inevitable appearance of those who would be Satanists has, I think, shown that in practice that if one wants attention the Devil is the last, best resort. However, none of these people have (aside, perhaps from the few authors that write for such an audience) improved thier lives significantly, never mind become rich, famous or sexually attractive which are, after all, the prime motivations for such 'believers'. In short it is all a bunch of bullshit. The fundamentalists who perpetuate the Devil are the best examples of the axiom of Levi and one is left to wonder if the fascination goes deeper than fear. As Blake said of Milton, it seems like they are of the Demon's party. They just won't admit it.

So much for the Devil. Crowley summarizes his thoughts on the subject of the Black Brothers and the Left-hand path in Magick Without Tears which is a collection of letters he wrote to a student of his late in life. I will produce the section from the book in which he discusses the Black Brothers, the Left-hand path and related matters.

Go to part 1