I sympathize with your suspicious attitude. I'd want to know a lot more about the assumptions of this study before I trusted it. I think it's important to distinguish between cultures that are unfriendly to outsiders, but very protective of one another, versus cultures that are friendly and open to outsiders in a nominal sense, but wouldn't be willing to devote personal resources to aiding them. Small town rural America (particularly in the deep South) is at one extreme, and suburbia/exurbia is at the other.

I also doubt social capital is a universal function. It seems likely that relative demographic correlation issues are quite important. If you are a Baptist and can join the local Baptist church, I'd bet Baptist churches in Alabama are as good or better than Baptist churches in San Francisco, and there are way more of them to choose from. On the other hand, if you're a Buddhist, San Francisco is going to give you a much deeper pool of resources.

If Phoenix disappears, it will no negative cultural impact upon the citizens of Tokyo & Hamburg.  Losing Los Angeles WILL have a cultural impact, but whether the impact of losing Hollywood would be negative is debateable.

This study states that the sun rises in the West and sets in the East.  Since this contradicts a lifetime of personal observations, it must be wrong.

The most likely cause for this "Sun rises in the West" conclusion must be anti-Southern bigotry common in some East & West Coast intellectual circles, with which I have a life time of experience.

One personal story.  In junior high & high school, I would read "Science", a high prestige scholarly journal.  I would ask my father about articles that I did not understand (and was interested in.  Many I did not understand but ... :-).

One paper did a statistical correlation between tornado fatalities/reported tornado vs church attendance and came to the conclusdion that those that went to church more would "trust in God" and not take proper safety precautions in a tornado warning,  I was aghast at the "conclusion".  I could think of 100 other reasons why the fatality rate woudl change (as you go further north, there is less solar heating and tornados are weaker.  Since population densities are higher in the north, and heating is more expensive, more homes have basements, etc.)  My father, a Professor of Statistics. explained that the study was EXTREMELY faulty and the only reason it got by peer review was due to anti-Southern bigotry.  One intellectual bigot wrote the paper and a couple more bigots reviewed it.  Since then I have seen many more cases of intellectual bigotry and this "study" just reeks of it.

BTW, my father was the first faculty sponser of the Black Student Association when it was formed at the University of Alabama.

On another level, the anti-Southern bigotry is so strong that my sister has to change her accent when she moved to Manhatten.

Mostly, I'm wondering how this "social capital" index was derived. I haven't read the book so I don't know, but I suspect the author started with the states he liked then picked the data (club membership, education, etc) to fit. In other words, we see the high correlation because the author used those factors to create his social capital numbers.

I've created a chart showing the relative goodness of ice cream. Rasberry vanilla swirl is white, cookies 'n' cream is pale green, fudge swirl chocolate with chocolate chips is dark green in my chart. And hey, look at the charts showing the correlation between chocolate content and goodness! Must be related. Of course it's related because  in my world "goodness" is measured by chocolate content. It's all circular and self-reinforcing, kind of like blogs tend to be.