Why does Oberon want Titania to wake and fall in love with some vile thing?
The whole play is an exploration of why people (and fairies) fall in love—an examination of the balance between irrational, emotional appeal and rational, social norms. The overlying mise-en-scene is the civilized union of Theseus and Hippolyta, while Oberon and Titania are natural forces, subliminal to the social order, in fact a threat to rationality—if Nature is upset, the human order will be upset also. By using the potion and upsetting the natural order (accidentally), Oberon is claiming dominion over the forest and the order of Nature. Between these two extremes—rational attraction with the bound of social order, and natural emotional order of nature, stands the troupe of rustics, who (it should be remembered) are rehearsing in the forest to perform at the “civilized” wedding. That the young couples courting (Lysander, Demetrius, Helena and Hermia) should also flee from civilization to the forest, completes the extended metaphor—love is partly rational and partly instinctive. Oberon, in tricking Titania, is showing that human control of the process is an illusion, and that attraction is also illusionary and subjective.