I think there's a difference between fearing a parent and fearing consequences. And that bit of fear of what will happen of you misbehave is what keeps kids in line - it certainly kept me in line as a kid!!
My mum would give us a good wanger if we misbehaved, my dad would give us the sad face and tell us he was disappointed. Personally I was afraid of both of these and indie as I was told (although my dad was worse). However you do it, the child needs to have respect for you and know your the boss.
My husband was beaten with a belt/broom/wooden spoon and that's jus going too far. When. We told them we were expected his dad said he'd go dig out his old belt - if anyone ever raised a weapon to hit my child I would hit the roof!
I believe it's more about personality and overall upbringing how a person turns out. I'm one of six and personally im gentle and socially awkward. All of my brothers and sisters are loud and confident and harsh - I have to be moral compas for all of them in one way or another. Some of them were smacked every five minutes, one of them was never smacked at all. I think for the most part we are who we are, regardless.
I think it's reasonable to smack a child's hand to stop them going for plug sockets/fires etc. other than that I'd like to think I won't smack him, but he's only 8 weeks old and don't have to consider discipline yet - ill just have to wait and see.