It is subtle and nuanced, but I think that the drama is more about the legal system and the notion of legal justice than moral terms such as "guilt" and "innocence." Juror Eight makes this known throughout the deliberations. The concept of "reasonable doubt" is where he focuses most of his arguments. Juror Eight does not really focus on the ideas of "guilt" or "innocence." He does not engage in moralism. Instead, his focus is legal and in line with the system of justice that has been established. The idea that "the defendant can be convicted only in the absence of reasonable doubt on the part of the jury" is something that guides Juror Eight's instruction. Juror Eight understands that the purpose of the jury is not to focus on "guilt" or "innocence" as much as reasonable doubt.
It is in this light where I think that the drama is more about reasonable doubt than the determination of guilt or innocence. The moral paradigm that guilt or innocence invokes cannot be reasonable adjudicated in the legal system. Juror Eight knows this and for this reason guides his analysis towards the issue of reasonable doubt. This becomes the basis of the deliberations and upon which I think the drama is more focused.