I think people are in different places in their heads at different times of their lives (i.e. teens, young adult, parenthood, middle age, etc...), and we all grow up with a different set of experiences and values; our parents, the things we watch on TV, our careers, the people we socialize with, our closest friends, genetics... everything can have an affect on how we gauge life. Seeking out happiness is very individual, and we do live in a society that doesn't necessarily discourage poor behavior. If your closest friends are all having affairs you might find it easier to participate, or at least come up with what seems like perfectly good reasons for engaging in one. Also, one can find ways to validate just about anything. Law is a perfect example of that!
There is no arriving, ever. It is all a continual becoming.