Ethnocentrism is viewing your own culture as more superior than any other culture (my definition from class :)) while cultural relativism is "the concept that the importance of a particular cultural idea varies from one society or societal subgroup to another, the view that ethical and moral standards are relative to what a particular society or culture believes to be good/bad, right/wrong."
Ethnocentrism is functional during times of crisis when the whole nation needs to come together and unite. It doesn't have to be against anyone or any other culture. It is also functional if it drives that certain ethnography or culture to have higher goals than any other groups and when they reach their goal it becomes a pioneer in that field. But when used to attack another culture, ethnocentrism is quite disruptive and extremely biased.