We, The Infected

Isn't Teresa sort of like a "completed" Oskar, had Eli not shown up and the bullies continued their merry activities?

Well, sort of, the stories are quite different, but there clearly seems to be a core of truth in that. Oskar and Teresa differ in the process of leaving the world, but the result is the same. A difference is that LS follows Teresa after she has left the world, while it is one of the last things happening in LTROI, leaving Oskar's fate to our imagination (i.e. in my book Oskar either will be forced back to our world by the cold, or else he will freeze to death or being turned).

A key difference is that, unlike the Wolves, and certainly unlike Teresa, Oskar and Eli never engage in violence without good reason - whacking Jonny is an open-and-shut case of self-defense, etc, and even the enraged Eli of the pool scene spares bystanders (Abby does kill everyone in sight, but it's not as if the world suffered much of a loss by it). Eli may be objectively the most dangerous of all, but the Wolves are worse. Theres does not seem as bad, because at least she targets people essentially randomly (somewhat like Eli) or those who have wronged her, and Theres can plead the insanity defense with considerable plausibility.

I see this as different reactions to similar processes in the two stories. One protagonanist being expelled from the society - "leaving the world" - meeting another protagonist that already is outside our world. John talk about meeting "the other", what happens when none of your templates applies, when you don't know how to act.
There also is a difference between contemplating murder (Oskar) and actually doing it (Teresa), but I don't place so much emphasize in this, since LTROI ends before we get to see what becomes of Oskar. The difference in age also plays a role here, we tend to be more forgiving towards kids than teenagers (Eli can kill, but not the wolf pack).

drakkar wrote:There also is a difference between contemplating murder (Oskar) and actually doing it (Teresa), but I don't place so much emphasize in this, since LTROI ends before we get to see what becomes of Oskar.

It's more than that, when push comes to shove, neither Eli nor Oskar relish violence, even if both are, to varying degrees, prepared to inflict it when necessary. Teresa is not like this from early on (remember the flies) and each step is merely the logical progression.
Of course, the distinction being made here is between being evil or vicious, and the rabid dog scenario - very dangerous, but not malicious. Teresa is clearly the former for me, Theres and Eli are closer to the latter.

drakkar wrote:The difference in age also plays a role here, we tend to be more forgiving towards kids than teenagers...

I don't think this distinction is unreasonable and, likewise, I think it entirely reasonable to hold adults to higher standards than teenagers (and of course children).

It could be a language issue, but I would not use the word "relish" about the violence in LS, it is pathological, committed by persons pushed over the edge by society. LS operates on a psychological level, where LTROI is more physical - Eli is a vampire and must kill for survival. In LS Theres and Teresa are mentally destroyed, driven to what they do on a psychological level. Theres is viciously violent already at very young age, without her "parents" doing anything about it.

drakkar wrote:It could be a language issue, but I would not use the word "relish" about the violence in LS, it is pathological, committed by persons pushed over the edge by society. LS operates on a psychological level, where LTROI is more physical - Eli is a vampire and must kill for survival. In LS Theres and Teresa are mentally destroyed, driven to what they do on a psychological level. Theres is viciously violent already at very young age, without her "parents" doing anything about it.

Setting aside the matter of causes for a moment (which for me seems to be a matter of blind fate) violence is described as an intoxicating experience. There is a tremendous high followed by profound depression. The ritual murder of Max the music promoter makes a good illustration.