I do disagree, actually. I think that stepparents are OBVIOUSLY entitled to have expectations about their role. My job was to communicate those expectations to my partner, and he decided if he could commit to marriage to me based on those expectations. Likewise, he needed to communicate his expectations to me, and I decided if I could commit based on his expectations. Just like any couple deciding to get married, I should think. In our case, that includes expectations about how much "mothering" of the kids I would do.
(It might surprise some people here to hear it, but it also included the expectation that this was a LEGITIMATE marriage, with all the same vows and intentions of permanance as any other/first marriage.)
The decision to "turn me into" a stepmother was made by my partner, based on what he wanted for his kids. Not on what his kids wanted. If he made his decisions based on what his kids wanted, instead of what he thought was best for them, he'd be a lousy dad.
Luckily for ALL of us, he thought having a stepmother would be best for them. I agreed. So that is what I am. Regardless, as you put it, of what the CHILDREN want or feel. The children also WANT and FEEL that they should eat crisps and bolognese for every meal, but we aren't flexible about that, either.
My role with my stepkids is WHATEVER role my DH and I agree on.