i'm a supporter of responsible spankings. the short analogy: you live in a house with some hazard, say a wood stove. you try to explain to your child rationally not to play around it, you try setting limits, having timeouts. you can't remove the hazard. ultimately i would claim that it is your obligation to inflict pain to communicate that danger. sometimes we need a physical reminder of our limits. *shrugs* i've long since resigned myself to being considered an asshole by others, whatever. there are times when spanking is appropriate.
of course, there are times when it is not. inconsistent spankings or spankings to relieve a parents anger are two obvious examples.