Analyze Stowe’s use of the motif of opposites/contrasts in Uncle Tom's Cabin. How do these opposites/contrasts advance or support some themes of the novel?

Stowe primarily contrasts slave owners, and this supports her anti-slavery theme. While in her time many people supported slavery by arguing that the majority of slaveowners were good to their slaves, Stowe shows that for every "decent" slaveowner, a cruel slaveowner exists. She is thus able to illustrate that the institution of slavery is flawed and evil, for it depends too wholly on the moral decency of the owner. If the master lacks decency, slaves suffer terribly and have no recourse.
For example, Stowe contrasts the master of Eliza's husband, George—who forces George to do menial labor when he is talented with machinery—with the kind Mrs. Shelby, who does what she can to nurture her slaves.
Stowe also contrasts Augustine St. Clare with his wife. Augustine is a decent if careless man, who understands the evils inherent in the institution of slavery. His wife, in contrast, does not believe in freeing slaves, doesn't believe slavery is evil, and lacks any empathy toward her slaves. She won't, for example, let her Mammy get any sleep at night, but also expects her to be up and active during the day, at her beck and call all the time. Mrs. St. Clare sends an impertinent female slave out to be whipped, despite Ophelia begging her to reconsider and suggesting that the slave will be raped at the whipping house. Ophelia is another contrast to Mrs. St. Clare, for she frees Topsy, whereas Mrs. St. Clare refuses to honor her late husband's promise to free Tom.
In yet a further contrast, Augustine's brother Alfred is cruel to his slaves. Additionally, in contrast to Eva, who treats the slaves with angelic kindness and love, Alfred's son Henrique hits his slave in the face with a whip to keep him in his place.
Finally, George Shelby, Mr. and Mrs. Shelby's son, who comes too late to rescue Tom, is a sharp contrast to Simon Legree, who beats Tom to death.
Stowe's point is that for every "good" master, there is a bad master. She asks, who, with a shred of decency, would leave another human being in the hands of a sadistic owner?