Gizmo, your post pretty much describes a situation I was in, except my mother was the one abused by Christians at her most vulnerable and I was the gothic daughter.
I also saw my first love emotionally destroyed and ultimately formed in the image of the abusers by a very f-ed up group of Christians. Somehow this hurt more than what they did to my mother, because she was at least an adult who had the right to leave, which she eventually woke up and made use of. They hurt her, but they didn't destroy her like they did him. She recovered and moved on with her emotional and spiritual growth. He gave in and decided it was easier to hate than to disobey. It was absolutely awful to see as they beat all the actual spirit out of him. I think I was one of the very last things he gave up in order to become the broken, twisted thing they wanted him to be.
He had to give me up because I was unbreakable when it came to indoctrination, even though I was only a child when they started trying. I'd already decided there was no such thing as an omnipotent, loving god, and nothing could shake me from that conviction. It's actually one of the few things I'm really proud of in my life--that I always stood up for what I knew was right (and wrong, lol), even when they were promising I could fit in if I just went along, and even when they were threatening me. Sadly, that didn't spare the people around me their abuse and manipulation.
To say I left that situation with a lot of anger at Christianity would be an understatement. I also, with all the logic of a 13yo, figured that if I was going to be accused of worshiping demons and corrupting the youth of the world with sex, drugs, and rock and roll that I ought to at least have the fun of actually doing it. I embraced doing every single thing they'd said was bad with great enthusiasm, and to this day think of myself as the "bad girl". I guess it became part of my identity somewhere along the way.
I did eventually realize that becoming what they hated was still giving them power and that the truest revenge would be to ignore them entirely and just do whatever felt right to me. I've lived that way for a lot of years now, and deal with proselytizing fundamentalists with all the energy they deserve. No debate, no striking fear into their hearts by invoking the names of demons (though that is terribly entertaining), I just say "you are nothing" and walk away. Because that's what Christianity has become to me--nothing. A non-entity unworthy of even discussing, a bug to be swatted at when it gets too close and otherwise ignored. The only reason I'm talking about it now is because I'm trying to sort through all the terrible things I've seen, and Spiritual Abuse was definitely one of them.
I do realize that this is why I avoid my fiance's family at all costs, though. We've been together the better part of a year and they have never heard my voice. I'll reluctantly text them if I have to, but otherwise avoid them completely. Because, while my fiance is as unrepentantly Pagan as I am, his family are very Christian. I know on the deeply emotional and irrational level of past trauma that they'll hate me and try to take him away, just like they did 15 years ago. No reassurance from him or even them will shake me from this. Deep inside I'm always snarling "you just TRY that shaming Christian sh*t again. I'm not 12 and helpless anymore."
Judging by the length of this post and the fact I'm shaking, I was a little more traumatized by witnessing all that Spiritual Abuse than I thought...