I think that helping your baby, toddler or child child to behave well involves a never-ending voyage of discovery. You have to learn as you go along, so it's right to question all forms of discipline or control, and discard the less effective ones.
There are just so many ways to control a child anyway. Personally, I put distraction, reasoning and rewards at the 'good' end of the spectrum, very closely followed by controlled crying and withdrawel of attention, then bribery - and shouting, smacking and sarcasm at the 'bad' end.
Each time I need to control my children, I'll use any one of these things, or a combination. I'm not perfect, just striving to be better. And of course some of the 'good' ways, like rewards, cannot be used too often, otherwise they are no longer as effective.
Although I have smacked my eldest I have seen that it is not a particularly effective form of punishment, except when it's an issue of serious safety. I'm trying extra hard not to resort to smacking with my youngest.
And pretty much the same goes for shouting at them, too. Personally, I feel a loud, prolonged shouting match with my son is a more violent and out of control method of discipline than a single light smack.
I have felt some guilt each time I've smacked my son, but I certainly don't feel guilt about my general approach to control. I think that as long as I strive to use 'good' forms of discipline with my sons, and follow this through, I am doing right by them.