Blended families can be a doozy. Remember the show Life With Derek? Or earlier than that, The Brady Bunch? The premise of both of those shows was bringing together two sets of kids when their parents remarried. Hilarity, hijinks, and buffoonery ensue when you bring together families through marriage. Not that it can't be a beautiful and healthy thing, but there are so many dynamics to consider. And kids are sensitive-- you have to introduce them to change in small doses. But adults are even more fragile, in my opinion. There are egos, past hurts, and adult feelings you have to factor into the branches of a blended family.
This recent Reddit story is a classic example of the kind of conflict that arises between divorced parents. It's a tale as old as time, but that doesn't make it any less infuriating.