"Hail Satan?" (2019)

[Belacqua]

That some author refers to obscure occult practices in France as "Satanism" doesn't make it so. Satanism was not a thing until LaVey created it as a philosophy. I don't know how many times I can repeat this. No one before LaVey called themselves "Satanists." It was a term that was used similar to "Pagans" or "heretics," almost exclusively by Christians.

Satanism "was a thing" at various times. I agree that LaVey organized it in a way that it had never been organized before. 

It was indeed a term used by Christians to attack people they suspected. There's a long interesting book from 1896 devoted to working out who really is and isn't a devil-worshipper. 

https://en.wikisource.org/wiki/Devil-Worship_in_France

It's true that Masons and others were accused of being Satanists, but weren't really. On the other hand, there were people who worshipped Satan, who were known as Satanists, and didn't reject the label. 

Again, I think you are using a very specific definition of the word which sees LaVey type people as the only true Satanists. This is of course the definition we would expect to find on the web site of LaVey's organization. Still, people who aren't devoted to LaVey tend to use the word in a more general sense, and have done so for a long time. And not only as a term applied to others, like pagan or heretic. This is supported by the sources I have given you.