'This is my truth, tell me yours' essentially.
People's culture, religion, upbringing, experience, personality etc dictates how they perceive everything and their morality stems from that.
Society as a whole in each country has established a set of basic rules upon which most people vaguely agree most of the time, but even that is open to reinterpretation, for example lots of people would have no qualms about murdering a child molester but they probably wouldn't murder most other people.