Trying to define the "Normal"

The Stranger has proven to be the toughest book of the semester for me to think about (and certainly to write/talk about). The complicated issue of murder aside, I really just don't know how to feel about Meursault. I've been trying to figure him out since I read the first three sentences, and I feel like I still haven't come to a consensus now that I've finished the novel. I almost feel bad, because I'm scrutinizing Meursault in the same way that the Algerian court is, by largely ignoring his crime and focusing on his character instead. But really I feel like I have to understand his character to some degree before I can understand his crime. So what follows is an attempt to understand why I feel so uncomfortable and confused about Meursault (and I don't think I'm the only conflicted one, right?).

I sort of have a theory, let's say theory-in-progress, that's based on the Platonic understanding of the individual (and Freud eventually develops a similar theory of the psyche, that I think is more well-known). Basically, there are three parts to a soul (Plato uses "soul" in The Republic, but the idea applies to human life on earth and is less spiritually related) which are the appetitive, the spirited, and the logical. The appetitive part consists of your elemental desire (food, water, sleep, sex, etc.); the spirited part contains your passion, emotions, the things that compel you to act; the logical part is your sense of reasoning, your rationale.

According to Plato, ideally the logical part of you should be in charge, and should also be allied with your spirited part to control the appetites. Internal conflict occurs in human beings when these parts are at odds with each other.

Okay, so the ideal person should be acting primarily using reasoning and partly using emotion, while paying moderate attention to their appetite. Can we say that this internal balance is representative of what a "normal" person acts like?

A large part of the prosecution's argument against Meursault is aiming to show how Meursault is not normal by showing how he is internally out of balance in this way. The prosecutors emphasize  Meursault's lack of emotion over his mother's death (which shows that Meursault's spirited part is missing in action) and explain that his murdering the Arab occurred without any reasoning on his part (which shows that the logical part of himself is not in command like it should be). This leaves his appetitive part to be in control, and Meursault even tells the reader that, "I explained to him, however, that my nature was such that my physical needs often got in the way of my feelings."

I think that because Meursault's personality doesn't fit the model by which a "normal" person is supposed to act, I feel (and the Algerian court feels) thrown off by his behavior in the novel and almost feel like there's something wrong with him. The prosecution argues that since his appetitive part is in control, he behaves outside the boundaries of reason without feeling any remorse and thus poses a threat to society (if he killed once and felt no guilt, then what stops him from killing again and again?)

As a reader of the novel, however, I get to see Meursault's story from his point of view, and for the most part Meursault's appetitive part rules his desire for simple pleasures (a swim on the beach, a night with Marie, a lazy afternoon of people-watching) and not violent inclinations. Meursault is made out to be "a monster," as the prosecutor says, by being accused of being so abnormal that he is a threat to society's well-being.