I also think it is illogical to expect a child not to push or hit other children if you're going to hit them when you're frustrated and upset.
I have also thought this, and now when I see how much my toddler copies mine and DH behavior and how quickly they pick things up - e.g. see things once and can then copy exactly - it has reinforced my belief that you need to behave the way you want your child to behave because that is the biggest influence on them. I was smacked as a child, never badly, and no it didn't harm me but I am quite quick to lash out and have smacked DD on one occasion and wished I hadn't, it is hard to restrain that urge and maybe if I hadn't been smacked then I wouldn't have that urge - who knows. Tonight she pinched her brothers nose because she was cross with me about not reading another story - I did restrain myself from giving her a smack - and after a few minutes of her screaming blue murder because I just left the room with DS - she calmed down and when I went back in she apologised and explained what she was apologising for - I am not sure I would have got that if I had smacked her.