I'm going to give my take on the whole thing (not that anyone has to read it!)
I have run the course of step parenting from the highest of highs to the lowest of lows.
At the start, I was young and had never been with someone who had a child so naturally, IMO, there were fuck ups on all sides.
I didn't know where I fit in. Sd didn't know what was happening in her ordered world and dh was understandably worried about sd's reactions to everything.
He was also, and I'm sure a lot of us have been here, worried about what ex would do.
I had an irrational anger and jealousy. I was angry "about" sd and all it entailed, but not "at" her and, in actual fact, I was angry at dh's burying his head in the sand instead of dealing with stuff!
Her early teens were the absolute worse. She lashed out. I was pissed off. Dh acted like a fucking child and her mum caused untold problems...
Except she didn't.
In hindsight, her mum did nothing more than try to support her daughter. It didn't help, but I don't think it was malicious.
I was extremely upset about some serious lies sd told me. But there was no real attempt on my part (when it first kicked off) to understand her, to really clam down and see what was going on.
You see? I wasn't a perfect SM. Very far from it.
But I learned. We all did. Now, we're great!
Look, when SM's come on here hating their sdc or wanting them out of the house etc, that's just not reasonable. I know because there were times that I was that SM.
And I can guarantee that if I hadn't had voices of reason telling me that blaming sd, or hating her, or banning her etc wasn't the way to fix it, I would not have a happy family today.
Sometimes support is about telling the poster here that she's wrong; no ifs or buts about it.
Yes SM come here in despair. I, for one, don't think telling them how saintly they are and how awful everyone else is, is being supportive.
It might make them feel better for the length of the thread, but real life has an awful habit of rolling on, regardless of what MN thinks.