when it comes to culture why someone believes that his or her culture is right?

People believe their culture is right because of something called cultural bias. That means that because people are raised and socialized under and within a particular culture they tend to see that cultures ways of doing things as the way things should be done.

Makes sense doesn't it? If you were raised that "this is the way to do things" then you would think that's the case

Everybody feels better within his or her own culture. Every culture has values to teach to the rest of us. Those who feel their culture is the only good one, are ignorant. But if they also want to impose it on the rest of us, then they should be place at the botton of the scale.

Because they know their own culture best and fear learning about others. Which reminds me of a quote from Shakespeare: Our doubts are traitors and make us lose the good we oft might win by fearing to attempt.