The evil step-parent or your child's new best adult pal? Which option would you choose for your child? Neither one may be desirable, however, I think most parents would choose the latter in favor of the evil thing.
Nevertheless, the over-stepping step-parent can become the proverbial stone in the shoe over time and cause great conflict on an ongoing and perpetual basis.
So what is "over-stepping?" That answer is in the eyes of the beholding parent. While there is no formula for evaluation of "over-stepping" I can offer a way to evaluate how to avoid conflict which negatively affects your child/children. Consider this approach:
1. WHAT DOES YOUR CO-PARENT SAY IS BOTHERING HIM/HER ABOUT THE STEP PARENT? If you don't have these specifics, its time for mediation or family counseling. Allowing the cold war to fester is a recipe for conflict.
2. MAKE A LIST OF THE STEP PARENT ISSUES. For example, is it ok to:
Coach a step-child's game? Once? Every Season?
Attend Parent-Teacher Conferences? What does the teacher say?
Have Unilateral discussions with other key Adults who are involved in the child's life?
Volunteer in the Step Child's Classroom?
Attend Field Trips?
Attend Back to School night?
Buy expensive gifts/clothes/gadgets for the step-child? What about expensive activities like football games?
Telephone the step-child for conversational purposes on an ongoing basis?
Plan birthday parties?
Post Social Media about "our" child?
Orchestrate school projects?
Takethe Child for haircuts? Ear-piercing? Tatoos?
3. DETERMINE WHICH PARENT WILL MEET THESE NEEDS IN THE FUTURE.
Don't "course correct" in the middle of a championship (or non-championship) hockey season.
If you believe that your child is unharmed by the conflict and hostilty then by all means, do nothing (said the Mediator sarcastically.) But, if you want to reduce conflict, doesn't Step 1 go a long way for putting YOU in control of reducing conflict?
In other words, if a parent feels the step-parent's role should not include step-parent's attendance on field trips, don't do it. Find other ways to have step-parent/step-child bonding; like movie time and board games or family vacations. I say "don't do it", NOT because it is wrong, or bad or negative. I say "don't do it" because "other parent" is upset. What is more important to the child? Having step-parent at the pumpkin farm field trip or avoiding conflict between the child's parents? Which would a child choose, NOT what would you choose is the real question.
That's why "fairness" or good intentions might not always matter. That's why "right and wrong" are irrelevant. That's why "best interest of the child" is the universal concept in family law matters. From a mediator's viewpoint, extra conflict for a child of divorce is always negative.
Of course all families are different and the circumstances in which the step-parent came to be the step-parent may be relevant. Did Parent marry Step-Parent after an affair that contributed to the end the marriage? Or is a Step-Parent bringing additional children into the family and merely attempting to create some sort of "equality" for the step-children? For example, if new step-parent has seasons' tickets to the Ravens' games, would the parent want the step-parent to exclude his or her Child from that event because it aroused jealousy in the parent? I didn't claim there was an easy answer, except that the decision should be jointly made and sometimes explanations provided. "So what should I do if I have an extra ticket and I'm taking my kids? Exclude your child and take one of my children's friends?" Sometimes such a conversation might provide perspective for the upset parent.
The answer is easy and hard. I think the answer is conflict avoidance and harmony among the adults who are the role models of the child. Determine the child's bests interests, but if you do so, place appropriate weight on the weight of an ongoing parental conflict upon the the child. To me that weight is very, very heavy.