It actually goes back to the Medieval period when music that was not church music nor followed the church's rules was the devil's music.
Madrigals were considered the devil's music because they were mostly about sex.
Ending a piece on a minor chord was also forbidden which gave us the Piccardi third (raising the third of the final chord of a piece in a minor
so it cold end on a major).
The tritone was also banned.
In modern and American terms, the blues was considered the devil's music by the African American religious community at the turn of the 20th century because of song content and that it was tied to drinking and dancing.
This was true of jazz and carried over to rock and roll.
The associations with drinking, dancing and sex were the original reasons.
Voodoo New Orleans musicians didn't help the cause nor did the fears of middle American about their white kids listening to "black" music.
Then there was Led Zeppelin and Black Sabbath....
music.stackexchange.com/users/2064/Michael Thibodeau
The first thing that comes to mind is «backmasked» messages (i. e. hidden by the means of recording it backwards) with sinister and supposedly satanic contents: http://www.religioustolerance.org/chr_cul5.htm
http://www.nauglefest.net/backmask.htm
The best example of such message is the classic passage from reversed «Stairway to Heaven»: "
All yours, here's to my sweet satan, The one who's little path would make me sad, who's power is fake.
He will give you, give you 666.
There was a little toolshed where he made us suffer, sad satan.
"
Listen to it: http://www.nauglefest.net/downloads/stairway_reverse.mp3
music.stackexchange.com/users/1698/Mischa Arefiev
Replying to Michael Thibodeau: I would love to see any reference to non-church music being called the devil's music during the medieval period that cites medieval sources.
I've been working on medieval music history for quite some time and never seen any reference to any of this history.
The reference to the tritone being the devil's interval can't be traced any further back than the 1700s.
See F.J.Smith, "Some aspects of the tritone [...]: the non-emergence of the Diabolus in musica " Journal of Musicological Research , 1979 for a complete debunking of this false tradition.
The avoidance of the melodic tritone in medieval music was for melodic, not theological grounds.
The practice of using tritones in melodic writing was actually freer in the late Middle Ages than later periods, with sonorities such as G-E-Bb with G in the bass considered as consonant as G-Eb-Bb or G-E-B.
music.stackexchange.com/users/5807/Michael Scott Cuthbert
Overly-broad question that's dangerously close to off-topic, but I have to quote this famous song from a pioneer in Christian rock, Larry Norman (1947-2008).
With lyrics.
The title quote, "Why should the Devil have all the good music"?
has been attributed to none other than Martin Luther(1483-1546)
music.stackexchange.com/users/None/
A key factor is that rock and roll made people move in ways that were not conducive to celibacy, ie they had fun concentrating on worldly things rather than spiritual.
Obviously this is the work of the devil. :-)
Nice screen grab, by the way.
music.stackexchange.com/users/104/Doktor Mayhem
Historically, what evidence has been cited in support of the claim that Rock 'n' Roll is the music of Devil? This notion exists in the popular culture, fueled by  Footloose  and half-remembered grade-school history, that there was some form of official religious condemnation of the rock-n-roll form. What's the real scoop?  On a related subject, was the interval of the tritone, the diminished fifth, really considered Devilish in the past?
What is the history of considering Rock 'n' Roll to be "the Devil's music"?
music.stackexchange.com
<history><rock-n-roll>
music.stackexchange.com/questions/9779
music.stackexchange.com/users/1344/luser droog
The avoidance of the melodic tritone in medieval music was for melodic, not theological grounds. The reference to the tritone being the devil's interval can't be traced any further back than the 1700s. In modern and American terms, the blues was considered the devil's music by the African American religious community at the turn of the 20th century because of song content and that it was tied to drinking and dancing. The association of rock 'n' roll with the Devil may in part be related to historical associations between the Devil and particular forms of music. However, it is also possible that it was more related to the association between rock 'n' roll and drinking, dancing and sex. If the tritone was considered 'the devil's interval', this was probably a recent concept as the tritone was originally objected to on melodic rather than theological grounds.
The association with rock 'n' roll being tagged as the Devil's music actually goes back to medieval times when non-church music was considered the Devil's. If the tritone was considered the devil's interval, it was a relatively recent concept as the tritone was objected to on melodic rather than theological grounds. Rock 'n' roll was generally considered the Devil's music because of its association with drinking, dancing and sex.