Capital Punishment

A member of parliament in the UK has called for the reintroduction of capital punishment.  See here.  Is this a good idea?  Before reaching any conclusions as to the desirability, or otherwise, of capital punishment, we need to be aware of a whole range of issues.

There's the issue of the purpose of executing. Is its purpose to act as a deterrent, or rather is its purpose an appropriate retribution or punishment instead?

Indeed, does it in fact deter? If it does, should we execute people if the net sum of peoples' lives are saved, even if we regard capital punishment as barbaric? Or if it does not deter, at least not significantly, is retribution or punishment enough of a justification for its reintroduction?  Regardless of whether the purpose is deterrence or retribution, how does the possibility of executing an innocent person effect our decision here?

What about the cost of keeping them in prison for many years compared to execution?

What about the issue of the ultimate origins of our behaviour? Are we mere meat robots whose behaviour is determined by physical laws rather than our conscious intentions? Even if, in a suitable sense, it is me that determines my behaviour, am I just purely a product of my environment? In other words are we born morally neutral?  If physical laws, or the environment, or both, wholly determines our behaviour then why would any punishment be justified?

 Alternatively, do we have free will and are we the type of people we are, at least in part, due to an innate component? That is say, do we self-determine to a degree how moral we are even though the environment and genetics plays a large role in influencing our behaviour too? 

Who should we execute? Anyone who illegally and with premeditation murders someone else? What about a woman who murders her husband as a result of being beat up by him day after day, year after year? Or murdering anyone who has made your life a living hell? What about murder due to a hopeless all-consuming jealousy?

Is executing, in fact, a greater punishment than spending many years languishing in prison? That also depends on what will actually happen to that person after death.