[some are] convinced that rock music is evil and will lead people to engage in witchcraft and draw pentagrams all over their home.
I think that it’s pretty safe to say that at least some people around you are stone-cold fundamentalists. This sort of discourse doesn’t come from non-fundamentalists.
That said as stupid as “rock is [from the d]evil” claim is, I don’t think that it’s rooted in racism. Instead I think that it’s because some values often followed by rock bands, singers and fans clash directly with some values of Christianity.
Note that some sort of percussion pops up in almost every musical style, across the eras.
Slaves. They created the guitar
This was already addressed, but… come on, acoustic guitars are from Middle Ages Iberia, and they backtrack all the way into the lutes of the Ancient Egypt and Anatolia. (Probably. It’s so old that the origins are hard to determine.)