Is a parent who chooses corporeal discipline because they consider it to be the best course of action given a situation - abusive?
Depends on the degree of the punishment, the age of the child, stage of development, how vulnerable the child is, and how resilient the child is. At best, spanking has been shown to be ineffective and neutral in it's ability to establish correct behavior long term. At worst, it not only humiliates a child and/or creates bitterness, resentment, and lack of respect, but can result in injury or medical intervention.
I've been looking at a comprehensive 20 year study done by the World Health Organization that sums up the various ways of child maltreatment and it's economic, social, and medical impact they have on people throughout their lives. It's a long study, but they do focus on not just corporal punishment, but sexual abuse, emotional abuse, and neglect in the various cultures and religious communities as well.
After I'm done, I'm moving on to the AAP and NIMH to round out the picture as according to what's done in the states.