@freemama Your situation sounds frustrating and no I'm not referring to that type of a situation. Our situation is flipped from yours. We have a very active Dad who takes the kids to do all sorts of activities and a Mom who doesn't sign the kids up for a darn thing. You are correct in that you should take into consideration your child's interest in a sport or activity. Not only is what is healthy for kids but its also going to help with that resentment issue you mentioned.
What I'm talking about are situations where one parent dominates and calls the shot on what activities the kid gets to do. He/She makes ALL decisions unilaterally without involving the other parent in that process. Doesn't make sure the other parent has the cycles to do it, doesn't make sure the other parent doesn't take issue with it on principle, doesn't care about the cost, doesn't care at all really what the other parent thinks. Even kids who are interested in softball or whatever have to get someone to agree to take them and support that activity for them. Mom or Dad still says Yes/No after weighing everything. We are talking about situations where the non custodial parent was completely cut out of that decision making process. And instead are told that this is what will happen and by the way it will also happen on your parenting time. And while this may sound extreme a number of folks on this board have reported that as being their experience.
When you have such a high degree of non cooperation and conflict in a co-parenting relationship your fallback is what family court has awarded each of you -- your parenting time based on your Final Orders. There are lots of divorced parents now who under the guise of "Best Interest of Kids" will attempt to call the shots. In healthy non divorced families you still have a discussion about whether or not it's okay to sign a kid up for a particular activity. The child doesn't automatically get to force a parent to agree to cheer leading, football, etc. just because it's in their "best interest." Conflict is also not in a child's best interest and dictating to your co-parent what the kids will do or not do will create conflict.
That battle cry of "This is in my child's best interest" is only going to get you so far in the co-parenting arena. Respect for you Ex's time/money, communication and minimizing conflict will get you much, much further.