OK, now I get it. It's about Chinese that travel abroad and then return to China with strange ideas, about democracy, free internet access to all websites etc. IMHO that's a good thing and in the long run will make life better for everybody in China. 

I think one of the reasons is that people only visit the touristical areas. If for example they only visit the centre of Amsterdam, then they think all Dutch smoke weed, and on every corner there is a red light district. Or if they visit keukenhof a agricultural area where they grow flowers, they might think we are into farming and growing flowers, while there are a whole bunch of other technologies. So as a tourist you have a very limited view, and it does not necerally gives you a better view than reading neutral info about the country.

I think if someone has the seeds of prejudice in them before visiting a foreign country, they're just going to go to the country and find things to confirm the opinions they had before coming. Just like if someone has the seeds of open mindedness and visits a country, they're going to look for all of the positive things to appreciate about a place. Travel is meant to test your assumptions about things and make you say "hey, I didn't know they did this in China" or "Hey, France wasn't as cold as I expected it to be." Travel challenges your assumptions. People who are prejudiced will be prejudiced no matter where they are. Its a mindset. 

I think that depends on the individuals perception. For me I use to think China was extremely dirty and filled with pollution and noisy people. But when I visited China partially it was true, especially the pollution, but I was distracted by the beautiful and enriching culture of china and was fascinated to see how people live in such busy areas. Now I don't just think about pollution and noise, which shouldnt be ignored as it is a major problem, but I picture the culture and beauty much more than the negatives. 

I would agree with the previous comments that a lot of people have closed minds before they travel.

Also:
Tourist visits are usually short and don't give time to really know a country.

Tourists don't really get a chance to talk to local people except waiters, tour guides and taxi drivers.

Parts of the tourist industry (souvenirs, travel brochures) prefer to reinforce stereotypes than explain the complexities of reality.

When they return home tourists prefer to explain exotic stereotypes than say that a lot of things are the same everywhere these days.

You could also add some more controversial arguments:

A lot of westerners like to travel to reinforce their view that they are more advanced than the rest of the world. Any love to explain to their friends back at home how less developed other countries are.

Some people like to fantasize that instead of tourists they are really 19th century upper class colonialists.

but depending on who your essay is for I wouldn't include these last 2 points in an English wrting exercise.