I think this arguement boils down to 2 things:

Is hitting and/or violence ever the correct response? I don't know about correct, but natural, illogical, and visceral, yes. If someone hits me, or treats me violently, I really want to hit back. Or run (ever heard of fight or flight?) When you have a two year old reaching for something that will harm them - like a hot plate or an electrical socket, my gut reaction is to smack the hand and say no. If all you do is speak, they may not hear, sometimes a physical response is necessary, even if it is just in the form of restraint (grabbing or holding a child rather than smacking). If none of us were ever done violently with, would this reduce or eliminate violence as a whole? I am not sure of that. There is in us, as people a deep visceral need to react physically, sometimes violently to actions. My opinion is this: sometimes spanking is necessary and it can be used for the good of the child. Sometimes it is used overmuch and does harm.

The flip side is, of course, are time outs and reasonable logical consequences, always the right course of action? As far as time outs go, the answer (mine at least) is emphatically not. look at the example above, of the two year old - they behaviour will cause the child harm, but putting him or her in time out will solve nothing. What consequences would there be? I am not advocating this approach exactly, but from many previous experiences have learned that many children will not understand something being hot until they experience the heat and pain for themselves. you may say, no, it's hot, but this means nothing until they learn what "hot" is. for actual bad behavior, like hitting or biting, etc, sometimes logic works, especially if the child has been on the receiving end of a hit or bite. As the child ages, the more often time-outs and logical consequences really are effectual. For children under the age of 3, really, not so much.

What my point is, is that regardless of your preferred method of discipline, you should always take pains to explain your actions. As briefly as possible, and as often as necessary. Sometimes hitting, smacking, spanking is the right way to go. Sometimes it does more harm than good. This is a debate I doubt will be resolved in my lifetime, but hopefully we can continue to discuss it like adults, with civility and logic, and without sarcasm and guile.