I would like to acknowledge and respond to GodzillasBumcheek's post though, because it is very considered and heartfelt and shouldn't be ignored.
I'm aware I am coming across as a holier-than-thou smug cow here, it's a price I've decided to pay to argue for something I believe in . As you've noticed my thinking on this issue is quite black and white - that's not because I'm a simpleton who can't appreciate subtleties, it's because after a HUGE amount of personal examination and soul-searching this issue is very clear-cut to me, and it's worth battling it out on these threads because people in vulnerable situations read them for advice.
However FWIW Godzilla (and I hope and assume you don't much give a fuck what I think of you anyway) OF COURSE I don't think you love your children any less than I love mine, or that you are generally a lousy parent. In various ways I am a lousy parent. I lost my temper and got cross and nasty with my 4yo the other day, because he had spread poo all over the bathroom. Actually he had had an accident and was trying to clear it up himself, because he didn't want me to be bothered by it while I was looking after ds2 who has chicken pox . Boy, did I feel like a mean, cruel, worthless murderess when I calmed down and realised how much I had upset him. I'm not sure that was any better than smacking. I have lots of difficulties with my kids, and I openly post about them on MN, I need help and advice as much as anyone else, and I don't hide from the fact that I am a decidedly less-than-perfect mother.
BUT - IMO I don't need to be perfect mother - or even have delusions of adequacy - to have a strong and forceful opinion on something as concrete as smacking. I argue against it every time, because I truly believe that it is the last vestige of legalised violence in our society, that it is indefensible and cruel. And I would rather be the kind of mother who fucks up by shouting/crying/saying something regrettable than the sort of mother who calmly and cold-bloodedly jits a little child and then justifies it to other people. A parent who lashes out and smacks, and then regrets it and apologises, is human IMO. It is an abusive act, but the parent who slips up like this isn't "an abuser", because this term implies regularity and intent. Shouting/frightening a child is also abusive IMO, and I've done that and don't know anyone who hasn't. The parent who decides to smack as a matter of policy, and can't see why it's wrong, is an abuser, pure and simple.