Has this experiment been repeated since? On kids who weren't growing up in the near aftermath of a great war?

Would you argue that there is some attribute that is fundamentally different between children growing up in the post WWII era and today (or any other era for that matter)? My very anecdotal evidence is that once any sort of division into groups occurs, children act in a matter very similar to the Ratters and Eagles. There was a gifted and talented program at my elementary school, which consisted of students from across the county who were bussed into the school and took classes seperately from other students. At the graduation pool party, an innocent slash contest escalated into a full out fight between over.. I'd say approximately 40 students, some of whom inflicted relatively significant injuries. Of course, in group bias had always existed throughout the school years, but violence associated with in group bias isn't something that I feel would be atypical in children of different eras.

Thank you for the reading suggestions! Perhaps my mind has already packaged Spock / lack of emotion into my understanding of the concept of 'Rationality.'

To respond directly -

Your purely emotion / empathetic desire for altruism governs setting your goals, your pure rational thinking governs how you go about reaching your goals.

Though if pure emotion / altruism sets my goals, the possibility of irrational / insignificant goals remains, no? If for example, I only follow pure emotion's path to... say... becoming an advocate for a community through politics, there is no 'check' on the rationality of pursuing a political career to achieve the most good (which again, is a goal that requires rational analysis)?

In HPMoR, characters are accused of being 'ambitious with no ambition' - setting my goals with empathetic desire for altruism would seem to put me in this camp.

Perhaps my goal, as I work my way through the sequences and the site, is to approach rationality as a tool / learning process of its own, and see how I can apply it to my life as I go. Halfway through typing this response, I found this quote from the Twelve Virtues of Rationality:

How can you improve your conception of rationality? Not by saying to yourself, “It is my duty to be rational.” By this you only enshrine your mistaken conception...Do not ask whether it is “the Way” to do this or that. Ask whether the sky is blue or green. If you speak overmuch of the Way you will not attain it.

I think one key in not being offended is being secure in your own person and position

I am very new to LW, but this seems like a dangerous position to take for a rationalist! From "What Do We Mean By 'Rationality'": [Italics Mine]

This is why we have a whole site called "Less Wrong", rather than simply stating the formal axioms and being done. There's a whole further art to finding the truth and accomplishing value from inside a human mind: we have to learn our own flaws, overcome our biases, prevent ourselves from self-deceiving, get ourselves into good emotional shape to confront the truth and do what needs doing, etcetera etcetera and so on.

It seems that being completely secure in a position makes it impossible to for you to challenge that position, which works against acting in a more rational fashion.

An alternative way to not be offended might be found here. In summary, the author argues that 'If people can't think clearly about anything that has become part of their identity, then all other things being equal, the best plan is to let as few things into your identity as possible.'

It's a well proven fact that many other people would not do that in the same situation

Do you have any sources that suggest that emotional reactions (such as ease of incitement to anger) are significantly different from individual to individual? I feel it more likely to be the case that you are still using the correspondence bias when you say that you'll kick the vending machine when "the bus was late, the train was early, my report is overdue, and now the damned vending machine has eaten my lunch money for the second day in a row" - these circumstances have provoked a emotion in you that you identify as anger. When you see a third party kicking a vending machine, attributing his action (kicking the machine) to a fundamental trait ("the man has an angry personality") is an example of the correspondence bias. People are less likely to think "that guy is having a bad day and the machine swallowed his last dollar" than "he is an angry person" because we attribute actions to personality traits in other people. You might be overvaluing genetics here.

There are whole countries full of people that would just feel sad, or blame themselves, or just let it go, or get only a little angry inside

I think that the correspondence bias is also displayed when we look at different countries or cultures. For example, traveling in Spain, one might think that Spaniards are warm loving people, because they make an effort to talk to tourists and communicate with them. Compare this to those who live in New York City, which has a reputation for curt, impolite citizens (probably because traffic is bad in the city, and everyone is trying to get to work ducking and weaving in between mobs of tourists who just get in the way - visitors to the city fall victim to the correspondence bias when thinking "New Yorkers are rude!").