Comment Google can help you here. (Score 1) 768
For reference, here is the text of the 5th amendment:
No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger; nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation.
So, to be clear, you only appear to be interested in one portion of it, the self-incrimination clause.
The purpose of this amendment, as written, was to prevent the government from abusing the legal process in such a way that no private individual could reasonably expect to prevail. All of the things that are prohibited in this amendment, were things that had actually happened to the colonists or their recent ancestors in England, so the concern was a very real one.
Let's take a brief break, and let me get something out of the way: You say "It would be disturbing to think that we've built a whole legal edifice in the United States (and many other countries) on a "right" that has no rational basis." - But you haven't done the most basic of research to discover what that is. Here's a link (PDF warning) to a examination of the events that led to the existence of the self-incrimination clause of the 5th amendment: http://scholarship.law.wm.edu/cgi/viewcontent.cgi?article=3341&context=wmlr Because you have said that links constitute a fail, (which is foolish of you), I will summarize:
In 15th and 16th century England, people were accused of a crime (Frequently it was that they were not strictly holding to the beliefs of Anglicism, which was interpreted as interpreted as treason against the King or Queen). When brought before a judicial authority, an oath was applied requiring that they answer all questions truthfully and completely - even if it incriminated themselves.
Then, one of two things would occur:
1) A fishing expedition, where questions would be asked until something was revealed that was a offence deemed worthy of punishment. (Damned if you do)
2) A refusal to take the oath. This was interpreted as directly denying the authority of the monarch (who had ostensibly given permission for such questions to be asked), and a charge of treason would be leveled, usually with a disproportionate punishment. (Damned if you don't)
So the end result was that the accused receives punishment. There was little possibility for a good outcome.
The 5th amendment exists to prevent the threat of disproportionate punishment for not answering questions from compelling a person to answer questions. It also prohibits the government from using a $5 wrench (http://xkcd.com/538/) on you - it follows directly from this amendment that the use of torture to compel information which could incriminate you is prohibited. (A prohibition against torture as a form of punishment is covered under the 8th amendment.)
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Now, to answer your questions:
The outcome in the world where we do have the Fifth Amendment, is clearly different from the outcome in a hypothetical world where the Fifth Amendment does not exist, even while holding all other assumptions constant.
You cannot be specifically punished (beyond the crime of which you have been found guilty) for refusing to testify. Without the 5th amendment, that would not be true.
The outcome in the "Fifth Amendment" world is better than the outcome in the "no Fifth Amendment" world:
Less use of $5 wrenches. Here's a test: If the outcome in a 5th amendment world is no better than the non-5th amendment world, why do people invoke it? Our justice system places a heavy emphasis on the presumption of innocence, and this clause exists to ensure that a person innocent of a crime would not have to provide the court with damaging knowledge that might wrongly result in a conviction.
The "benefit" can't be something that benefits all suspects equally, whether they're innocent, guilty of violating a just law, or guilty of violating an unjust law. Several people have brought up to me the example of the McCarthy hearings, when those being questioned cited the Fifth Amendment as the basis for refusing to answer red-hunt questions.
The "benefit" can't be something that exists separately from the Fifth Amendment right against self-incrimination. I've had it suggested to me that without the Fifth Amendment, the police would just beat people into confessing. But of course the right not to be beaten by the police is separate from the right to remain silent.
You are wrong about this. The text of interest is this: "nor shall be compelled in any criminal case to be a witness against himself". If you examine the appropriate definition of "compel" you will see that the 5th amendment specifically prohibits the use of threats, torture, or other methods of compulsion to get a person to testify against themselves. The right not to be beaten with the intent to compel answers is explicitly the purpose of this amendment
If the argument has major implications for the competency of the courts generally, then address those implications. This is not really a "pass/fail" criterion, because implications can be open-ended.
A few things to keep in mind: With enough compulsion, the accused can be made to admit anything. We place great weight on confessions. If we are permitted to compel confessions, a prosecutor can simply wait (while the accused is "compelled" ) until they have a confession that fits the their version of the story, and present it to a jury. In effect, the 5th amendment prevents the prime witness from lying to the court. If you don't thing this has implications for the competency of the courts, then we're done here.