To me, I see the idea of using "bio" and "step" as a move towards equalizing the titles. They are both "mom", one is just "bio" and one is just "step". And I have to admit, if my kid had a stepmom who wanted to be equal with me in parenting my kid, Id be mad. I'm the mama, not her. I would want to just be "mom" and have the stepmom refer to herself as a stepmom. It seems like that is where a lot of people are coming from when they always get irritated about this language on this board. Even if it is selfish and wrong to feel that way.
This is a really good point.
It made me reflect that perhaps "bio" and "step" seem "logical and grammatical" to me because I spend a lot more time with my step-son and do a lot more of the conventional "mothering" work than his Mom does. However, she was still his primary caregiver the first 8 years of his life and he still loves and is bonded to her, so she - and she alone - is and always will be his Mom. Intellectually, I'm very clear on that fact. But in day-to-day life, I'm just as involved in caring for him as I am for my own kids (more so, because my older sons spend a lot of time with their Dad). Meanwhile, Mom's interaction with DSS is (by her own choice) largely limited to a phone call every 3-10 days and spending vacations with him. Understandably - but still falsely - I often feel like an equal mother to him, or even more of one. I should watch that.
And furthermore, my own kids have a stepmother, but she has become a true friend and I don't feel threatened, devalued, or disrespected by her in any way. That, too, is unusual. If I had more typical tension with her, I might feel more sensitive about the idea of being called "bio" mom.
Sorry! Back to the real issue...