Depending on when their relationship started, it's pretty plausible that a teenage girl could be enamored and abused by someone like Manson who certainly had a lot of power both in wealth and as an influencer. He was still able to make money selling CDs so he probably did better than most.
These things are always difficult because here we are 15 years later with little evidence and no other corroborating accusers. So you have to look at their motivations and if there's any room for misunderstanding or different interpretations of the events that happened.
You see it as close mindedness and ignorance because you lack in knowledge. Those "puritans" fighting back at rock and roll back in the days knew exactly what rock music stood for. They weren't ignorant or dumb, they were more informed than the people listening to it.
They just knew how to recognize it because their religion warned them exactly of what rock and roll brought to the table, and now look what rock and roll has evolved into. Guys with leather costumes and painted faces playing horrendous noise while screeching about how they hate christianity or God. I used to listen to metal and think nothing of it as I got into more and more extreme metal, but once you see it for what it actually is you grow a distaste for it and realize that those people are 100% unironically worshipping satan.
en.wikipedia.org
I know you're a Muslim but literally every Christian church I've attended in the past decade or more has had some form of rock band leading the worship service. Yeah they're not playing thrash metal but people in the 50s and 60s would have clutched pearls about it.
Rock and roll is also about as dead as disco so it didn't really evolve into anything other than more country or hipster music. It peaked in "hard" with nu metal in the late 90s and early 00s and got absorbed into other genres. Metal itself went pretty underground over the past couple decades when it couldn't cling onto the nu metal acts anymore.
That all said - sometimes song lyrics are an act and sometimes they're coming from a legitimate place. Rammstein and Metallica are two of my favorite bands and like 95% of the time their lyrics are edgy nonsense and I'm just there for the overall sound. In this particular case, maybe some of the more graphic sexuality Manson portrayed in his music had some truth to it?