Ok, normally I try not to go off topic on a thread, but I just want to address a couple of things that Davy brought up.
First, the term "step parent" was not coined by the feminists or by our current pro-mother legal system. It's been used since around the 8th century. It can be found in old english texts, and equivalents of the term have been found in Latin, German, Norse Chinese and Japanese languages. There are plenty of uses of the term that can be found in 18th century literature that we're all familiar with - like Grimm's Fairy Tales.
Also, I take issue with your statement that we should have a mindset that "excludes elevating a spouse to the special class of a parent". Because, while I may not have physically given birth to my step-children, I am just as much of a parent as someone who adopts a child. I do all of the "parent things" when the children are here 50-60% of the year. I get them up for and take them to school, I help them with their homework when my husband has to work late. I cook for them and clean up after them. I am the only person who's EVER taken them to get haircuts. I teach them manners, I help them negotiate problems they have with each other, with their mom, with their friends. I support their relationship with their father. I have taught them how to take care of "female" things, and how to wash their hair, how to shave their legs, even how to wipe properly. I comfort them when they wake up in the middle of the night from a nightmare or growing pains. I put them to bed at night. My father put money in an educational trust for them when they go to college, just as he did for his biological grandchildren. I could go on, but I think you get the point.
I do all of the same things a parent does. I worry about them as though they were my own, and I love them as though they were my own. And, a lot of what I do, is because their biological mother does not. And the kids know who does all of these things for them - there's no confusion there, or conflict coming from the kids. The conflict comes in when the biological mother gets territorial. I have never tried to take over for her. I take care of the kids the best way I know how, when they are with us. She does not take care of them when they are with her, and then gets pissed when I do it.
Case in point... when SD1 was around 12 years old she started asking for deoderant. I knew this was going to be a "hot button issue" with their mom, so I told her to tell her mom. For a month, every time I saw them she would ask. I would tell her to ask her mom, and she would say that she had asked her, but she won't buy it for her. So I finally bought her some. The minute I did that, we started getting the nasty e-mails - seven of them, to be exact - accusing me of having "empty womb syndrome" and trying to "steal the kids" from her, and saying that SD1 never asked for it, that I was "forcing her to wear it against SD1's wishes" and "demanding" that I stop trying to "force her" to wear deoderant. This is totally typical of the way things go with her. She doesn't do stuff, doesn't do stuff, doesn't do stuff... then when I finally do it, I'm a horrible person who's trying to steal the kids.