I think we're talking past one another here. Or maybe it's me mixing things up. As I knew the fifth amendment, it related to dealing with the police in all circumstances, but you're saying that this is unrelated to the fifth amendment? If you're right that the fifth amendment only applies in court, and the right to remain silent is indeed a separate one, then that's my mistake.
The Fifth Amendment:
Amendment 5 - Trial and Punishment, Compensation for Takings. Ratified 12/15/1791.
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.
The principle is the same in most democratic countries; the wording differs slightly. In all cases, this provision exists only during court proceedings. A person has no Fifth Amendment rights in their interactions with law enforcement outside of court testimony. As for invoking this right, the actual procedure varies by country. In the United States, the person does not give evidence (testify) with respect to the material covered by the Fifth Amendment. In Canada, your section 13 invocation is acknowledged by the judge and you must the testify anyway - the caveat is that the evidence you give may not be used directly against you in any criminal proceeding with the exception of perjury.
"The right to remain silent" is a different legal right, which is only afforded to persons under arrest or detention. If you have not been detained or arrest by a law enforcement official, you do NOT have the right to remain silent when asked a question. You may choose to remain so, but if the officer has a legal provision which allows them to 'demand' (a legal term) a response, you must give one. Several pieces of legislation may include these provisions, most frequently laws which govern customs, immigration, and other types of inspectors.
As for the rest of your responses, I'm not going to beat what-ifs to death. I will address one in particular, though:
5 - As far as I've seen, the supposed criminal is always the one viewed with scorn, whether by the judge or the jury.
How many preliminary hearings, trials, voir dires, pre-sentencing hearings, and sentencing hearings have you attended? How many witnesses in general have you seen testify in court proceedings? How many law enforcement officials have you seen testify at court proceedings? How many court transcripts and case judgments (and I don't mean in the media summaries, I mean actual official judgments and transcripts) have you read? Reading a media story about a trial and reading the trial transcript or actually attending it are two very different things. Judges afford witnesses just as much or more credibility as police officer until they're given a reason to view it otherwise.
Suffice it to say that all law enforcement are ultimately accountable to their fellow officers, superiors, the justice system and judiciary, and the public at large, whether you believe them to be or not. Perhaps your country is different and has serious problems with its police force (I honestly don't know), but that doesn't give you the grounds to judge law enforcement the world over by their actions.