In a comment to an essay I posted last night, ruidh wrote: "You seem to be hung up on the sin = wrongful act definition. This really causes no end of problems. ... Sin is not failing to conform to some external yardstick. It is failing to live in relationship with God.
Defining sin as the failure to live in relationship with God has a nice ring to it. But it doesn't seem to be especially useful. Doing so would require us to make a couple of crucial determinations, discussed below. Unfortunately, I don't know how to make those determinations, and I can't see that anyone else does either — at least not with sufficient confidence that I'd be willing, on that basis, to label others as sinful in some particular respect.