Why is ethnocentrism bad?

Ethnocentrism leads us to make false assumptions about cultural differences. We are ethnocentric when we use our cultural norms to make generalizations about other peoples' cultures and customs. Such generalizations -- often made without a conscious awareness that we've used our culture as a universal yardstick -- can be way off base and cause us to misjudge other peoples. Ethnocentrism also distorts communication between human beings.

Ethnocentric thinking causes us to make wrong assumptions about other people because . . .
Ethnocentrism leads us to make premature judgments.

"They" may not be very good at what we are best at.

By evaluating "them" by what we are best at, we miss the many other aspects of life that they often handle more competently than we do.

Some very simple examples of ethnocentric thinking. . .
We often talk about British drivers driving "on the wrong side" of the road. Why not just say "opposite side" or even "left hand side"?

We talk about written Hebrew as reading "backward." Why not just say "from right to left" or "in the opposite direction from English."

We encourage SNU students going on short-term missions to use the phrase "Oh, that's different" rather than more pejorative terms when encountering strange customs or foods.


Xenocentrism
The opposite of ethnocentrism is xenocentrism which means preferring ideas and things from other cultures over ideas and things from your own culture. At the heart of xenocentrism is an assumption that other cultures are superior to your own.

reference
http://home.snu.edu/~HCULBERT/ethno.htm