I think the phrase that suits your thoughts is 'to broaden one's horizons'. I agree people can live in their culture and not question its values, or their values. However, even people who have lived abroad and experienced another culture may not necessarily 'broaden their horizons'. Rather one possible outcome among others, is that they may become even more convinced of their previous ways of doing things and/or thinking!

I am deeply convinced that people are easy to get lost in their own culture without contacting outside culture. Most people immersed in their own culture cannot find what they are . They are likely to  be obsessed by their education , family or personal experience  . That is why I consider people can travel overseas to look what exotic people are doing . 

when we want to know the nature, we use science as a tool,such as maths,physics, chemistry,etc.When we want to know the cultures, what can we use? It seems everyone can talk about culture.We need all sorts of tools such as cultural anthropology, psychology,philosophy,knowledge of history and religions.especially comparision knowledge of different cultures.It is not enough if we only have experiences for the culture itself through our five sences and thinking abilities.

  I am confident in  my knowledge as to my  identity.

As for others,  I cannot answer for them.

Yes, i questioned myself sometimes, if a particalur culture maybe reasonably described in 'absolute' terms, not in 'realative' ones?

I mean, it's hard to say anything about the culture of the Earth if you have never met an extraterrrestrial. Or to speak about Chinese if you've never been travelling abroad. When you cann't compare?

But does it mean there actually no 'absolute' measure, i.e. not based on comparison?