i guess it's difficult for me to know about other people. i was wondering if it's a difference between europeans and americans (since for europeans, "abroad" is much closer). but isn't america a varied place with different cultures in different states?
maybe another way of making my point is that the kind of people whose mind is most likely to be be broadened by travel are already aware of the kind of issues you might think they would learn. while those so closed they don't get it, won't - travel or not... your argument only seems (to me) to apply to the lucky few who are closed-minded at home, but open-minded enough to suddenly change when the food is different or the people don't react the way they're used to.
There are a lot of different cultures in the U.S., but I think the biggest differences aren't the regional ones, and imo hard to get a feel for just by traveling. The lives and cultures of people living in rural areas vs. urban areas, wealthy vs. poor areas, nearly-100%-white vs. nearly-100%-black areas, etc., etc. are all very different, but they aren't primarily state-to-state variations. For example, I found living in Houston and Chicago to be not that different: I lived in a middle-class suburban area in both, and their culture was more "middle-class suburban American" culture than any kind of distinctively Midwestern or Texan culture. I think there's some of that in cities, too: SF and Portland and parts of Manhattan have more in common with each other than with some places that are geographically much closer to them.
Living in a different one of those cultures can be very educational, but it's somewhat hard to break into unless you have some organic reason to be there or social connection. People are often resentful of "lifestyle tourism", the stereotypical one being an upper-middle-class white kid who moves to a poor minority neighborhood as a cultural experience. Small rural communities can also be quite closed as well, in terms of being able to really join the culture (vs. just visit the town).
America's culture does differ from place to place, but it's all under the same umbrella, and has only been growing for a few hundred years. It lacks the long span of history and conflict that a lot of the rest of the world has.
I think that experience is the best teacher. Whether or not you think you understand issues, or think you are experienced enough to deal with certain situations, you don't know that until you are put in those situations or confronted with those issues.
I also think it's a mistake to say that people are binary "close minded at home" and "open minded" outside. People have a range of experiences and impressions that colors every interaction they have.
maybe another way of making my point is that the kind of people whose mind is most likely to be be broadened by travel are already aware of the kind of issues you might think they would learn. while those so closed they don't get it, won't - travel or not... your argument only seems (to me) to apply to the lucky few who are closed-minded at home, but open-minded enough to suddenly change when the food is different or the people don't react the way they're used to.