Thoughts on sin

I've spoken in the past about how easy it is to see other people's sins but not our own.  This is one of the points made in a prayer we make during Lent.  We pray that God would help us see our own sin and help us not to judge our brother.
One thing has come to light on this regard.  How often do we look at someone else's sins and think, "How can they be so blind so as to do that sin?"  Of course, when we look at ourselves, we are much more gracious, merciful and compassionate.  We can offer many explanations and reasons for why we sin and how the sins we do are really not that bad.  Of course, such sophistry is nonsense.  All sin is bad and ought to be hated.
But back to the question.  How is it that some people do sins x,y and z and somehow excuse or justify it, when someone else, often times very similar in class and culture, sees that sin as horrible and ridiculous?  I believe it has to do with environment and genetics.  When we grow up in a family where certain sins are coddled or excused, we learn to do the same thing.  We, as fallen men in a fallen culture, from fallen peoples, have genetic predispositions toward certain sins.  (One example that I know of is the weakness towards alcohol among the American natives.)
Of course, neither of these are excuses for sin, but understanding them help us to respond better. 
So we should recognize that the sins we see as so obviously wrong, someone else, for complex reasons, does not see it that way. 
This all goes back to our tendency to judge others and go easy on ourselves.  We go easy because we know the details of our own lives.  Really this comes down to community.  When we spend time with and genuinely get to know others, it is natural to have compassion on them.  It's easy to chastise and judge the other guy, whom we do not know.
It's becoming more and more clear that community is incredibly valuable.