I believe that part of the outcome has to do with the childs environment. Just because both parents are present doesnt mean its a healthy situation. Some couples stay together for sake of the kids. That can back fire if the child witnesses an insincere 'togetherness" he or she may rebel to possibly bring the parents closer. Ultimately spending too much time worrying about adult problems.
a child needs both parents.and children who are raised by both parents are generally better in life.but this doesnt neccessarily mean that a child raised by a single parent will turn out awful.in some cases,they can be better than some who are raised by both parents.it depends on the overall environment.
In a perfect world everyone would get two loving, attentive parents. Does anybody live there? Clearly, there are plenty of single parents who have raised plenty of happy, healthy adults as have the married couples. All parents and families need support instead of getting pitted against each other as if one group is somehow "ideal".