Why is talking about spanking so divisive?

Why can it be so difficult to talk with people who were spanked as children about the fact that spanking has been found to be harmful and not actually effective at teaching children good behavior? Why is even suggesting this might be true met with hostility and defensiveness (never mind outright stating it)? If people want what's best for children, and I don't doubt people in these conversations do, then why does the disagreement reach such high levels of angry opposition to even considering alternatives to spanking?

Of course, many people who were spanked will claim that it worked out fine for them, taught they "respect" and "consequences," so the risks must be overblown or completely untrue. This is an illogical conclusion since a few anecdotes are never enough to completely overturn a measurable trend, never mind that they may simply be unaware of the harmful effects it had on them personally, but I question just why are they holding on to irrational conclusions? What is the motivation to try to justify this conclusion?

I think the answer is in their justifications. They don't typically argue that hitting children is OK, and will even sometimes go so far as to try to claim that "spanking," or whatever other term they choose to use, is somehow not "hitting." So they know using violence against children is wrong; they simply refuse to see spanking as violent, and they look to their own upbringing for justification.

This, I think, is the key to their defense of spanking. They're not simply defending their own parenting abilities - many of these people are not even parents themselves. Instead, they are defending their own parents.

People who love their parents and had a happy childhood with them are going to usually reject the idea that anything their parents did could be interpreted as abusive. Abuse is something "bad" people do, people who don't love or care about their children. Real harm is done on purpose, not by accident, by loving parents who didn't know better. Loving parents aren't ignorant of how to raise their kids!

This positive view of one's own parents seems normal, but add the stated goals of spanking - respect (for parental authority) and consequences (for challenging parental authority) - and it becomes even more difficult to think critically about one's own parents! Respecting parents in this mindset means trusting that they know best, not challenging parents, enforced through painful "consequences" that are framed as logical, natural outcomes of not "respecting" "authority."

Of course in this environment, where spanking is used to reinforce this kind of unquestioning "authority" of parents, breaking out of the mindset that respect and love means supporting and obeying parents and instead recognizing that it's OK to question and doubt your parents, even to say that they're wrong, is going to be a difficult challenge. The more spanking was taught at the way to raise children to love their parents, the more difficult it's going to be to convince someone who does love their parents that spanking isn't likely the reason they do.