An eye for an eye makes the world blind, and the others committing wrong doings does not justify another person committing a wrongdoing. There are other ways of punishing people or insuring that they feel guilt and remorse, and coporal punishment should not be used as a tactic on adult offenders.
Corporal punishment for adult offenders is ethically wrong. I think that corporal punishment is torture and it should never be used for punishment. The only time that it could possibly be for the good is when someone knows something that could help save the life of innocent people in a timely manner.
Corporal punishment for adult offenders is as ethically wrong as it is for juvenile offenders. There should be no physical violence put upon one human being upon another human being period, much less a government or corporate entity upon another human being. They committed this crime, but we are smart enough to realize that there is more than eye for an eye.
Corporal punishment is alright for some adult offenders if the crime fits the punishment. If it was a sex crime then corporal punishment would be alright because this would really emberass the offender and that is what we want. If would be tough to determine who would administer the punishment but it could be worked out.
Corporal punishment is not unethical for adults. Some people are inherently violent and will not be rehabilitated. The only acceptable punishment is removing that person from society. When society has given up on rehabilitation, the only answer is corporal punishment. That is where the ethics apply. Knowing the difference between someone who is worthy of the effort. Not everyone is.