"One of the rare advantages to not being so is that occasionally those in charge do the morally right thing despite the majority opinion."
Quoted for truth. The seemingly emotive nature of support for the death penalty is in itself a good reason not to introduce it.
AOG:
"Why is it that Right-Wing are the most interested for it to be re-introduced, but generally it is rejected by the Left-Wing? "
As this thread will no doubt demonstrate, there's not one answer to the question - lots of arguments are put forward against it (as with arguments for it), and people will vary in which they find most persuasive.
Personally? I tend to waver a little on this issue, but I'm certainly against using it in any kind of 'mainstream' way if that makes sense - i.e. any regular, repeated or systematic way. The only kind of circumstance in which I'd possibly be persuaded to support it is in very rare cases like those of dangerous psychopaths, where there's no sign so far of any kind of possible 'cure' so far, and any solution other than containment just seems to make them more effective. John Douglas (the founder of the FBI's profiling unit) is very persuasive on this point - there are instances, as he demonstrates, where serial killers who are genuinely insane or psychopathic are simply beyond reform given the current state of our knowledge.
But even if that were introduced, it would have no meaningful impact in the way that most proponents of capital punishment hope for (i.e. no deterrent, not really much satisfaction or justice - just a situation where there doesn't seem much alternative).
That kind of capital punishment - the more widespread model designed to deter violent crime - I'm utterly unconvinced by. It's understanding of deterrence is simplistic and to me seems inaccurate and incomplete. It also ignores the unacceptably high rate of wrongful convictions (for instance even my limited system above would likely have killed Colin Stagg).