Children emulate the behavior of their parents, violence is a language, children won't learn to be violent if they don't experience it. The contradiction of being told hitting is wrong and being hit is mentally destructive. It comes down to whether violence is right or wrong. It's hypocritical to tell your child violence is bad and then later on go and hit them. It's a contradiction. Standards are universal, if the standard is violence is bad then it's bad, no exceptions. Respect teaches respect just as violence teaches violence.
Christians too often don't treat children as rational beings, like equals capable of discussion, understanding and mutual agreement and mutual respect. That's not to say you can truly have a relationship of equality with your child because they are completely dependent on you, but it does mean that we need to understand that every relationship must have reciprocal values. That means if the standard is that you can hit them then it would be wrong to say they can't hit you. Because the development of the mind is so vital to behavior and cognitive reasoning ability it's imperative that parents avoid as much as possible placing contradictions into our children's minds.
Violence begets violence and understanding begets understanding. Violence is a language. If you have no discipline that is very unhealthy, obviously, but hitting is not discipline. Of course the obvious flaw in spanking as a method for correcting behavior is the frequency with which it appears to be needed. Persuasion will always win out over force, and when discipline is necessary there are in infinite amount of options at your disposal. Hitting is lazy because you don't want to think of a more effective alternative and it shows a lack of creativity in how you handle a situation. Hitting should never be an option if your intelligent enough to come up with an alternative and calm enough not have hitting be your natural reaction. I know I may sound harsh and critical and I apologize, but I think it's important to get rid of this mindset that hitting is somehow the only way to handle kids, or that it is in some way more appropriate than hitting a spouse or brother or parent or co-worker or anyone else in your life.
The parent-child relationship is the only relationship in the world which one party has no option of disassociation. The relationship of child to parent is essentially a state of involuntary dependency. Therefore, any aggression by the parent toward the child - whether in the form of verbal or physical violence; or, physical or emotional withdrawal, constitutes a violation of and an abuse of that relationship. In other words, it is the obligation of the parent, to insure that the child's experience of the relationship were as if it were voluntary.
There is only incentive and compulsion (or the threat of compulsion). Incentive must be the primary method of behavior modification. Since children are designed to emulate the parent, the most effective method of teaching desired behavior, is to model that behavior. This means: behavior modification is first and foremost, an obligation on the parent, not the child. Incentive is not the removal of a negative, the removal of a negative is not a positive. -1 + 1 = 0. A child must be shown why it is a positive value to behave a certain way.
The imposition of will, as a parent, is a necessity - but only validly so, in circumstances in which it is clear that the child would agree (when old enough), that it was indeed in their best interest. Such cases might include interventions to insure the immediate safety of the child, or the regulation and maintenance of the optimum health of the child, long-term. In addition, this standard goes both ways: the parent is obligated to anticipate choices for the family that, while inconvenient or uncomfortable for the adult, are directed toward satisfying the mental and emotional needs of the child (something they presumably would also grant ex-post facto permission for).
Children are a fountain of natural wisdom, from which parents can augment and expand their own learning and growth process. Without the humility to ask the question, "what can I learn from my child", both parent and child suffer. This kind of humility is another way in which the parent can create opportunities for the child to contribute in meaningful ways to the family.