THE POWER OF SIN IS CENTRIFUGAL. When at work in a human life, it tends to push everything out toward the periphery. Bits and pieces go flying off until only the core is left. Eventually bits and pieces of the core itself go flying off until in the end nothing at all is left. "The wages of sin is death" is Saint Paul's way of saying the same thing.
Other people and (if you happen to believe in God) God or (if you happen not to) the world, society, nature—whatever you call the greater whole of which you're part—sin is whatever you do, or fail to do, that pushes them away, that widens the gap between you and them and also the gaps within your self.
For example, the sin of the Pharisee is not just (a) his holier-than-thou attitude, which pushes other people away, but (b) his secret suspicion that his own holiness is deficient too, which pushes part of himself away, and (c) his possibly not so subconscious feeling that anybody who expects him to be all that holy must be a cosmic SOB, which pushes Guess Who away.
Sex is sinful to the degree that, instead of drawing you closer to other human beings in their humanness, it unites bodies but leaves the lives inside them hungrier and more alone than before.
Religion and unreligion are both sinful to the degree that they widen the gap between you and the people who don't share your views.
The word charity illustrates the insidiousness of sin. From meaning "a free and loving gift" it has come to mean "a demeaning handout."
Original sin means we all originate out of a sinful world, which taints us from the word go. We all tend to make ourselves the center of the universe, pushing away centrifugally from that center everything that seems to impede its freewheeling. More even than hunger, poverty, or disease, it is what Jesus said he came to save the world from.