Joseph, since you bring this up again, yes there is potential for great harm. It is a potential choking hazard, it is a potential hazard if the bottle falls from its prop, it’s a hazard of damage to the teeth when they emerge, and most important it is crucial hazard to the baby’s emotional development.
A parent who will prop a bottle regularly, may also not be holding the baby during other parts of the day. Babies physically and emotionally need one on one physical contact. True, it does not have to be the mom, but that is certainly the ideal. So if the mother for whatever reason cannot regularly hold her baby, she should find someone else, who will.