Why is it seen as wrong in the US to hit your own kids ?!?

Don't you think it's a bit unfair to place a scene filmed in the 1960s timeline, a very different time era, on the same level as today's American post-modern culture? Filming the slap to make the dad look bad was appropriate and intentional for a nostalic period where things were pure and innocent and any murder would immediately make it to the front page news (unlike today where a murder would either go unnoticed or be found in small article in the back section of the newspaper) and, I think, for the purposes of showing the kind of reaction one would typically give in 1960s American urban culture. I think neither lack of reason, or the presence of feelings and even nurture is a helpful way of studying the totality of an American individual's mannerisms. Culture and identity also might have something to do with it.

The only thing hitting a kid proves is that you're too impatient to talk to them and you breed a cycle of learning that we hit things that anger us, maybe just maybe if we can teach our kids to talk through their issues they'll grow up where violence isn't an acceptable response and if we do that maybe we'll make the world a safer place for everybody.

I know this post is old but I just came across it and thought I'd share my opinion.
I agree with others who have said that hitting doesn't help most of the time.

I think the context and the way the child is hit is important. Slapping your daughter across the face is different to giving your child a smack on the hand. The former is totally uncalled for, teaches the child nothing about behaviour and only creates a divide in the relationship between parent and child.

I was personally smacked many times when I was a child, mostly by my father. My father wasn't some physically abusive monster, he just gave out smacks for misbehaviour and defiance. However these smacks were ultimately ineffective. I can't remember what I was smacked for, all I remember is the fear and the shame. I remember the angry look on my father's face and how much I resented him every time he'd hit me for committing some small wrong.
On the other hand, I can remember the lessons I was taught when my mother would scold me, take away my priviliges or express her disappointment in me. I know to respect other people's belongings because when I broke my younger brother's TMNT truck, my mum's look of absolute disappointment coupled with her asking me how I would feel if someone had broken my favourite toy allowed me to understand what I had done wrong. I was learning a lesson and I was being listened to. I was punished but I also had the hope that things would get better. It posed a challenge to persevere and that if I could make it through that grounding, time out, etc I would become a better person at the end of it.

All my dad's smacking did was cause me to become bitter and angry. It taught me to be scared and not speak my mind for fear of offending someone. It also drove home the message that violence was a way to control people, that I could use it if I wanted to but only on smaller people so that it would work.

You guys need to know that abuse is wrong and illegal.