Rational behavior as human beings

If you cross the country, you encounter a culturally different concept which may be created by humans' illusion.

We have different laws in each country.
Speaking of the United States, they have different criteria in each state.
People are easily confused about what is a right thing in the world. It happens in a daily life that the legal behavior a parson does in a country is considered as illegal in another country.

Where do the ideas of law come from?
They should be related with politics, economics, and environment.
The significant idea based on law must come from conscience.
Conscience must be the same in each person all over the world.
Obviously each person has a totally different thought in his mind because he experiences distinctive things because a status he has, a place where he grows, and a distinctive group of people he is involved in influence his way of thinking in his entire life.
So each person may have different conscience. I believe, however, we have a common sense despite a different background.

People sometimes prefer to do a bad thing which they know clearly is not a good thing for themselves and for evaluation from society, whereas some of them who especially have a strong own faith really hate a bad behavior.

If you think the behavior your friend does is illegal but the behavior happens as a normal thing inside the culture while it is extremely criticized in your country, what do you do there?
You are in a different culture but considering humans' conscience, you know it is not good for your friend.
How can you convince her or him to understand what she or he does is a seriously bad thing she or he has to stop?
Your friend doesn't know a serious situation where she or he are.
Do you decide not to say anything to her or him?

And if you encounter the situation where you are forced to do the same thing, how can you behave? Your friend may not understand what you say though you want to reject it.
You can decide what to do in each moment. However, in order to insist on your opinion, you need to persuade your friend that your idea is right enough.

Why are you be with friend?
She is just one of my many friends but a precious friend.