The subtle effect of this is to decrease some stress - always a benefit in supporting labor. If stress is reduced than so are levels of hormones that interfere with oxytocin production. This attitude keeps women shackeled to a mode of care which undermines confidence that their bodies work. But you don't usually need morphine to deal with a sprained ankle. Yet they do not view the process as one of unendurable agony.
Epidurals have side effects that do cause problems for many moms and babys.
These tend to be downplayed as of little consequence when a doctor or nurse is explaining the epidural to a woman in labor. But the problems caused are significant. They interfere with the progress of labor to such a degree that a woman has a greater risk of having to have a c-section or forceps or vacuum assisted delivery. All of these have added risk for injury to baby or mom. Studies have now shown babies can have feeding difficulties for up to a week after birth.