Under no circumstances should capital punishment be condoned. It is a barbaric form of punishment, which serves no useful purpose as it obviously does not act as a deterrent. In the USA, for example, the use of capital punishment increased greatly during the eighties and the nineties but with no corresponding effect on the crime rate. Another argument says that it effectively deals with people who are a danger to society. But in any case, they spend years, even decades, on death row while their appeals are used up, and might as well just be sentenced to life imprisonment with no possibility of parole.
The system by which people are convicted is simply not as foolproof as some people would have us believe, and the odds against an innocent person being killed are just too high. While the risk of this happening remains a very real possibility, the death sentence is unacceptable. In this age of DNA evidence, many people in American prisons awaiting execution have been found to be innocent. The other problem is prejudice. Even if a person is found guilty and convicted of a crime, they are likely to get a worse sentence if they are from an ethnic minority, and proportionately large numbers of these people are executed every year in the States.