What themes/quotes would you use to compare A Streetcar Named Desire and The Duchess of Malfi?

Tennessee Williams's A Streetcar Named Desire and John Webster's The Duchess of Malfi possess one major theme in common: sin.
In Streetcar, sin is evident in two of the main characters, Blanche and Stanley. Blanche's sin becomes evident when readers learn of her life of sexual promiscuity. She has given into lust (one of the Seven Deadly Sins) and sleeps with many men, assumedly sometimes for money. Now, some may argue that Blanche does so in order to survive; yet, arguably, this does not truly excuse her sinful ways. Stanley is also lustful, and he is also abusive (which one could align with the sin of wrath). Stanley is a womanizer, rapes Blanche, and physically abuses his wife.
In The Duchess, sin (more specifically greed, another of the Seven Deadly Sins) is present in the Cardinal and the Duke (Ferdinand). Both men try to talk the Duchess out of remarrying because they wish to take possession of her fortunes.
A second theme present in both plays is class structure. In Streetcar, Blanche constantly reminds Stella, her sister, that Stanley's class is below theirs. Likewise, in The Duchess, the Duchess's brothers are angry that she pursued and married a man beneath her (their) station.