What is the theme of "Good People" by David Foster Wallace?

 One theme in the short story "Good People" is the crisis of conscience. 

The story's omniscient narrator focuses on the thoughts of Lane Dean and his perception of his relationship with his girlfriend. As they sit on the top of a picnic table with their feet on the bench, Lane watches Sheri sigh with the weight of deciding whether to have an abortion: 

The whole thing felt balanced on a knife or wire; if he moved to put his arm up or touch her the whole thing could tip over. 

As his girlfriend sits quietly with her thoughts, Lane wrestles with his conscience. He feels guilty for being so "frozen" about this matter. He is trying not to be involved in the consequences that he perceives as influencing his girlfriend's life much more than his.

He pretended it had no name. He pretended that not saying aloud what he knew to be right and true was for her sake, was for the sake of her needs. 

Finally, after a lengthy examination of his conscience

...two great and terrible armies within himself, opposed and facing each other, silent—

Lane realizes that he shares responsibility for the situation as much as his girlfriend. So, her moral dilemma is his dilemma, as well. He realizes that he has been hypocritical and selfish to have considered things to be solely decided by Sheri. Watching his girlfriend, Lane recognizes his obligations to her. He knows that she may absolve him of them by declaring that she will have the baby, after all, and raise it by herself. However, he cannot let her do this; he must share with her the responsibility for their actions.

There on the table, neither frozen nor yet moving, Lane Dean, Jr., sees all this, and is moved with pity, and also with something more, something...that is given to him in the form of a question....Why is one kind of love any different? What if he has no earthly idea what love is?

Lane considers the possibility that he does love Sheri after all, and he simply has not recognized his feelings as just another kind of love from what he has imagined. As Lane acknowledges his feelings for Sheri, he takes her hand and prays for the courage to meet the truth.