In a small town like Jefferson, everyone's up in everyone else's business, which makes privacy difficult. The town is also extremely judgmental, and Light in August is set in 1920s America, so things are a lot more conservative. This conservatism leads Joanna Burden and Hightower into their roles as outsiders – Joanna is an outsider because of her progressive views and because she never marries, while Hightower is cast out of the church because of his wife's adultery and death. Both of these characters struggle against the societies in which they live but they also remain somewhat loyal to them, refusing to leave the town of Jefferson since it's the only town they've ever known. In this sense, they embody the struggle between the individual and his or her surroundings.
The characters that don't conform to societal expectations are punished in one way or another.
Happiness in Light in August is associated with living in society, not apart from it.