Let me start by saying that it is by no means the case that rates of infection increase with length of time after membrane rupture if examining fingers, monitoring devices, tampons, whatever are kept out of the vagina--or even if they are not. (Women who test positive for GBS may be exceptions to this, but even their babies are fine provided they get their antibiotics onboard.) It is also possible that a brewing infection breaches membranes and releases the fluid rather than vice versa, especially with preterm rupture of membranes.
Returning to your question of the problem with prolonged labor with intact membranes, it isn't that there is inherent risk in some preset amount of time passing, but of how well the baby is tolerating a lengthy labor and whether something is keeping the baby from coming out no matter how much time is given or what is tried (obstructed labor). Obstructed labor during the pushing phase can injure the pelvic floor, leading to fistulas. This is a big problem in developing countries where malnourished women are married and having children too young to have fully developed pelvises and who live in rural villages and must travel for hours or days to get to a hospital with cesarean capability. And, of course, where there is no timely access to cesarean surgery, a baby who is not tolerating labor will die.
In short, how long is too long is a judgment call. Unfortunately for women in most developed countries, it is a call usually made well before it needs to be.
P.S. It troubles me that you called yourself "stupid." Besides not being true, it isn't good for us to put these kinds of labels on ourselves. I invite you to pay attention to occasions when you put yourself down and to substitute more positive messages. If you wouldn’t say it to your friend or your child, then don’t say it to yourself.
. . . I now believe that the whole thing boils down to whether or not we trust a woman and her body to take good care of her baby. The belief that the birthing woman is an inherently dangerous place for baby to be leads to the popularization of diagnoses such as dystocia. Separating mother from child is crucial to promoting our societal message that the baby in fact does not belong to mother but to institutional safeguards of society such as the hospital. Tienchin