When you're a little girl, you don't dream your prince on a white horse may have a pony or two behind him, carrying the kids he's already had. And you probably don't realize, after you marry your prince, that in a lot of people's eyes you are suddenly The Bad Guy. There's a term for you, missy, and it starts with "evil" or "wicked".
I have it good, because I'm married to a guy who is a great father, who doesn't expect me to be a mother to his kids. The kids are people I like; smart and funny, their mother has her own life, and I have a studio where I can go hide. And it took me a long time to get to this point.
Not everyone has it so good. This week on Dear Prudence a woman wrote in about her stepson driving her nuts, and she got torn a new one. Now, this lady may have phrased it badly (or, I suspect, was edited to sound worse than she was), but what I read is not the ravings of a monster but a woman who is trying and floundering, and expressing some valid resentment.
The thing is, a biomother can complain about her children from dawn till dusk (as long as she adds the disclaimer "it's all worth it" at the end), but don't let a stepmother ever indicate that taking care of someone else's kids isn't the Best Thing Ever, or suddenly she's got a house made of candy and a stove warming up.
Stepfamilies take years to "settle". It's not easy, and it's not black and white. Amazingly, there may not actually be a "bad guy" in most step situations.
Men and women marry, have children, and often divorce. Unless a divorced or single parent expects to stay single for the rest of their lives, stepparents are a reality. Fathers, don't expect your second wife to mother children that aren't hers, and mothers...you may also be a stepmother some day, so don't assume the worst about the women who already are.