It is a well established principle of law that when weighing the evidence the fact finder must not subject each piece of evidence to the standard of proof (proof beyond a reasonable doubt). The trier of fact must apply that standard of proof to the whole of the evidence. Defence counsel do not want judges rejecting evidence by subjecting each piece of evidence to the "reasonable doubt" standard. That is a sure way for the prosecutor to set aside an acquittal on appeal.
How is this a "well established principle of law"?
If each piece of evidence individually doesn't meet a reasonable doubt standard, then how could they possibly meet it when combined?