Personally I think spanking is acceptable if it is issued swiftly, over the clothes and only when the child has done something dangerous. That being said, it's never been effective with our son. A time out has proven 10x as effective so we don't bother with spanking.
I don't think that a spanking in and of itself is a form of child abuse but has the potential to become abuse if not used within strict guidelines for the disciplinarian. If a spanking, regardless of how it issued, becomes the first line of discipline instead of a last resort, one could be treading in dangerous waters. I will rarely spank my children, but have no difficulty in doing so when all other discipline tactics I have employed have failed to produce the required result. Abuse, in it's many forms, is a matter of overwhelming and overpowering another human being (even children) which gives the abuser a (false) sense of superiority, in my humble opinion. Discipline, should be meted out in a manner that takes a child's age, mentality and the offense into consideration when deciding an appropriate action/consequence. I usually think about my child's unique personality and what works best with each of them as a guide to decide on an appropriate punishment for the offense.Just my two cents....
Spanking and abusive hitting are two different things. One is done because you love your child and you want them to learn there is consequences for bad behavior. Abuse is done in anger. One should never discipline a child in anger. We discipline and teach them because we love them.
There is nothing abusive to me in spanking a young child with an open hand on the bottom. When it comes out of anger and a need to exert power over another with the intent to physically or emotionally harm a child, it crosses the line to abuse. I spanked my daughters rarely, because a stern voice usually was enough. My son has such a high threshold of pain, that a pop on the bottom didn't phase him, so I rarely spanked him either.