Yes, I do agree with the statement, as do I'm sure most do. But where people differ is where they place the line between justice and vengeance, and that's probably a more important topic of philosophical discussion.

I would say generally, yes. Again, every nation's judicial system champions justice, it's just that some nations' ideas of "Justice" (North Korea for example), may be perceived as vengeance or cruel and unusual to others. But the idea of justice is still there.

I have some pretty limited experience in law (I took some courses in high school as well as partaking in mock trial competitions), but from what I learned, the Supreme Court has ruled in cases questioning capital punishment for minors and the mentally insane, that the bearing in which we measure 'cruel and unusual' depends on the current level of progression in today's society, and such punishments that are generally rejected by society's standards for retribution are to be determined as severe and therefore unconstitutional under the Eighth Amendment of the US Constitution.

So I think the more important ethics question you should be asking is where we draw the line. The problem is that so many people differ especially in the case of capital punishment. If we were to determine whether execution is 'cruel and unusual' by the bearings we (Americans and the Supreme Court) measured it before when considering the execution of minors and the insane/retarded, then I think it would be generally ruled as vengeance and not justice; since the United States is (I believe) the last western post-industrial nation to uphold the death penalty.

So to answer your question I believe that it can be applied only by today's standards of ethics, which in itself if very arbitrary and elastic. So is the idea of justice something practical? Yes. But is the principle of true justice to be practically applied in the judicial system in all aspects? I would say a soft no. Generally speaking we can, and do; but in all reality morals are relative, and to some people certain perceived 'justice' is really vengeance.

You also have the problem in law of the idea of deterrence. Retribution is only half of the equation. Many of the world's judicial system is set up on a basis of retribution and deterrence. The former being punishment and the latter being so that others are discouraged of committing the said crime. I personally believe that once the judicial balance is more geared toward deterrence, that punishments are more cruel and unusual and are more considered 'vengeance'.