This comment by Jeremiah Bowden at the very least offers a curt explanation of its obscurity (page 10):
Nietzsche is especially vehement in his denunciation of the Christian view of sex...
Moreover, in his "Law Against Christianity", a piece that was eliminated from numerous editions of The Antichrist because of its virulence, Nietzsche proposes that, "The preacher of chastity is a public incitement to anti-nature. Contempt for sexuality, making it unclean with the concept of 'uncleanliness‘, these are the real sins against the holy spirit of life."
Fortunately the citation notes indicate which edition of "The Anti-Christ" the quote came from:
Friedrich Nietzsche, “Law Against Christianity,” in The Anti-Christ, Ecce Homo, Twilight of the Idols, and Other Writings eds. Aaron Ridley and Judith Norman, trans. Judith Norman (New York: Cambridge University Press,2005), 67.
And that edition I found here: http://krishnamurti.abundanthope.org/index_htm_files/The-Anti-Christ-Ecce-Homo-Twilight-Of-The-Idols-And-Other-Writings-by-Nietzsche.pdf
In particular the article is on page 66-67.
Law against Christianity
Given on the Day of Salvation, on the first day of the year one (-30 September 1888, according to the false calculation of time)
War to the death against vice: the vice is Christianity
First proposition. - Every type of anti-nature is a vice. The priest is the most vicious type of person: he teaches anti-nature. Priests are not to be reasoned with, they are to be locked up.
Second proposition. - Any participation in church services is an attack on public morality. One should be harsher with Protestants than with Catholics, harsher with liberal Protestants than with orthodox ones. The criminality of being Christian increases with your proximity to science. The criminal of criminals is consequently the philosopher.
Third proposition. - The execrable location where Christianity brooded over its basilisk eggs should be razed to the ground and, being the depraved spot on earth, it should be the horror of all posterity. Poisonous snakes should be bred on top of it.
Fourth proposition. - The preacher of chastity is a public incitement to anti-nature. Contempt for sexuality, making it unclean with the concept of 'uncleanliness', these are the real sins against the holy spirit of life.
Fifth proposition. - Eating at the same table as a priest ostracizes: you are excommunicated from honest society. The priest is our Chandala, - he should be ostracized, starved, driven into every type of desert.
Sixth proposition. - The 'holy' history should be called by the name it deserves, the accursed history; the words 'God', 'saviour', 'redeemer', 'saint' should be used as terms of abuse, to signify criminals.
Seventh proposition. - The rest follows from this.
Obviously tho, the work has been supressed for this:
The criminal of criminals is consequently the philosopher.