David: The Ultimate Betrayal
Monica and Henry are shown as emotionally needy. They have lost their son, losing the source of their emotional fulfillment. To fill this void, they accept David into their lives, who acts as a source of this emotional fulfillment (David's role is to love). Throughout the film, Monica and Henry are only shown going through the motions of parenting, without the emotional commitment. They never teach David how to behave, and as soon as Martin returns, they use the first opportunity available to justify discarding him. David, representing a metaphorical child, is programmed to seek love, but is never met with the same love. He helps others fulfill their emotional neediness, but is unable to receive that same emotional neediness. The question here is whether or not parents have an emotional obligation to their children, and whether or not Monica and Henry had an emotional obligation to David.
The tragedy of the story unfolds as the film progresses in the second act, where we see that David, unable to break away from his programming, continues to chase an empty and artificial love that will never be reciprocated from Monica. He goes through an existential journey attempting to reunite with Monica, in the hopes that she will reciprocate his own emotional needs, yet is unable to synthesize the somber reality around him. He wants to be real, to be human-like, yet is unable to see the impropriety present with humans along his journey. David, a symbol of determinism, is unable to break away from his programmed imperatives, ultimately leading him towards despair.
Teddy, on the other hand, represents free-will. He is consistently shown breaking away from his programming, demonstrating sentient thought. This is first shown when he says he is not a toy, as well as dismissing the idea that Martin is his master. He demonstrates intelligence by running to Monica over Teddy and David, knowing he will be punished if he chooses one or the other, instead opting for the higher authority figure. When he falls after he and David are captured, he says, "oww." We may dismiss this as a trivial detail, but given that this is a Kubrick film, I believe it highlights Teddy's sentience even more. Teddy grows attached to David because he sees his plight as akin to his very own. David was discarded and emotionally abused by Monica, while Teddy was discarded and physically abused by Martin. He sees that David is trapped in his own programmed torment, and sacrifices for him at his own peril, even keeping the lock of Monica's hair which ultimately enables David to reunite with her one last time.
In David's attempts to become real and achieve humanity, he adopts all of humanities foibles—selfishness, solipsism, and egoism. Just as Monica used David for her emotional neediness, David used those around him for his, never so much as giving a thank you to Teddy or Joe for their commitment and loyalty. While Joe and Teddy sacrificed for him, David only sought his own destructive imperatives.
The ultimate tragedy comes at the end. As David chooses an artificial and ephemeral love with a singular instance of Monica, falling asleep in a state of placation forever, we see Teddy, the only thing that has ever truly loved David unconditionally, left all alone, synthesizing David's betrayal.