One of the reasons Rose chose to cast his 1954 television play with twelve men (instead of a mix of women and men, which he later did do later on) is that, according to the prefatory material in the front of the Penguin Classics edition, is that he sat on a jury in a murder case in 1954 (the same year in which he wrote the play) and was deeply impressed by the fact that the eleven jurors he was with could argue "bitterly for eight hours" and then bring in a "unanimous verdict." He was so overwhelmed by the power of the experience, sitting in the midst of the group of twelve angry men arguing themselves to the point of shared "reasonable doubt" or jointly rejected doubt that he was inspired, if not compelled, to put the experience in writing since it was such a "powerful situation."
nothing stands between the person in the box and the horror of an unchecked government except twelve diverse, reasonably intelligent people. (Reginald Rose, Introduction to Twelve Angry Men)
Having twelve angry men instead of twelve women and men (in the initial performances) helps you to understand the play, for one reason, because it helps you to envision and voyeuristically participate in the epiphany Rose himself experience during the jury room process of going from total dissent, total disunity, total individual vehemence to accord, unity and resolution. In other words, Rose takes you to the jury room along with him.
Over time, we see, the reasonable often find a way to unite the seemingly irreconcilable claims of passion. (Reginald Rose, Introduction to Twelve Angry Men)
The intention of Reginald Rose's Twelve Angry Men is highlighted in the title. Rose has made it clear that, whilst prejudice, expectations and personal issues all play a part in the conflicts and ultimate resolution, it is the masculine arch type that is being examined, in various forms.
Typically, at the onset, the male jurors want to establish their dominance. There is no place for emotional displays so feelings or pity have no real place. Men need to be decisive; hence the annoyance when juror 8 is able to make other jurors question the defendant's possible innocence. Looking at worse-case scenarios is a typical male trait which ensures they are always right and always prepared: "Suppose you talk us outta this and the kid really did knife his father?" A man, stereotypically would not wish to be proved wrong and it can be best avoided by convicting the boy. Then no-one will ever know so, for a very typical male this would be a win-win situation. The boy who will be executed is a by-product and immaterial to the greater good that will be served! (in the mind of the juror)
Twelve Angry Men also examines the fact that men often act irrationally and only consider the situation afterwards when they are more rational. Juror 8 is almost a conscience-like persona that ensures that all the male issues (despite his reasons) that are displayed in this play, are not allowed to ultimately control the outcome as they may have done in a personal one-on-one situation.
These men represent the worst and best (in the end) of male characteristics, making the audience understand the intention of this play is not to prove a man innocent or guilty but to reveal the potential in all of them; even juror 3.