'Sin' is not just a classification for certain types of actions. 'Sin' is a curse placed on humanity for "disobeying God" in a singular instance of satisfying the insatiable curiosity God created us with.
Allegedly our most primitive ancestors were placed in a garden and told that we were not to eat of the fruit of one tree which grew in the midst (the very centre) of that garden. As if that were not enough to drive them completely mad God also saw fit to place a talking snake in the garden along with them insuring our destiny and sealing our fate.
Somehow we were supposed to know better before eating from the tree of the knowledge of good and evil, right from wrong. Yet some of us still reject the dictates passed down by self-appointed authority figures who obviously don't have a clue as to what the hell they are doing.