This is the famous”Golden Thread” that runs through the criminal law of the English-speaking world. An accused person is presumed innocent until proven guilty according to law in a fair and public hearing of an independent tribunal. This means that you cannot call a person guilty for a crime before you have all the proof that will eventually prove that hi is guilty of that crime. So, if you cannot prove that a person is actually guilty, he has all the freedom to walk out a free man.
The accused person must know what he or she is charged with, so that full “answer and defence” can be made. This means that there must be enough “particulars” (details as to time and place, acts complained of, damage caused, Criminal Code sections violated, etc.) in the charge to avoid unfair surprises at trial.
Generally, an accused person is entitled to be in court for the whole trial, as well as for any preliminary hearings, so as to be able to confront his or her accuser, and to make full answer and defence.
Generally, too, a trial is open to the public. This is important if justice is to be “seen to be done”, even though it can sometimes be painful or embarrassing for some of the people involved.
What this means is: since the Crown has brought this accusation to the court, the person it is accusing does not have to say a word in his or her defence until the Crown has placed evidence before the court which, if accepted, could justify a conviction. The prosecutor, in effect, has to justify the charge before the accused has to answer it.
Further, the prosecutor must prove the Crown’s case beyond a reasonable doubt. The judge or jury is not just to decide whether the accused is more likely guilty or more likely innocent. There must be convincing proof of guilt. Of course, there might always be some tiny doubt, but for this to result in an acquittal, it must come from something more solid than mere speculation.
As for people who think rules like this favour the accused too much, they should perhaps bear in mind that we are still convicting a significant number of innocent people.