This is where you are horribly misinformed about what makes our legal system run. I posed the question about a defendant "speaking up" to my wife, a lawyer, and this is her response:
o Once on the stand the prosecution can ask your client about all
kinds of other stuff that may make your client look like a major
asshole, but that really don't prove he committed the crime.
However, once stuff comes out of your client's mouth that makes
him look like a schmo, the damage to the jury is done. No matter
if the judge instructs the jury not to consider the witness's
statements in reaching their verdict, they're really going to.
That's why attorneys ask questions they know they're not allowed
to ask--the witness will answer before their attorney can stop
them, and the damage is done.
o Your client might make an awful witness. He could be extremely
nervous, or extremely cocky, etc. Once a bad impression is made
on the jury, you have a tremendous uphill battle.
o And of course, the whole idea that you are innocent until
proven guilty. The prosecution has to prove beyond a shadow of a
doubt that the defendant committed the crime. This is a
tremendous burden to meet --- the hardest one in our entire legal
system. Most of the time, the prosecution can't do this without
information from the defendant. If the defendant never confessed
to the police or anyone else about the crime, and was not caught
"red-handed", you certainly don't want to hand your client over
to the prosecution on a silver platter by putting them on the
stand. You're supposed to zealously represent your client, and
part of this means making the prosecution prove its case, i.e.,
making them work and jump through all the hoops for a conviction.
This is one reason why so many battles in criminal law are over
the legality of police searches and interrogations. If anything
about it was illegal, the prosecution can't use the fruits of the
search or an interrogation confession. The prosecution has to get
a conviction without any help from the defendant.
Your credulous acceptance of what the prosecution has asserted (their "narrative", as if it were as straightforward as that) is curious for someone professing to be interested in the truth of the matter, not to mention your confusion between notions of "factual problems" and "analysis presented of what those facts mean".
Bill