'Sin' has become an old-fashioned word. One reason for this is that sin is a religious word. It suggests that what one does wrong is wrong in the sight of God. Another reason is that the word 'sin' implies that there are some things that are absolutely wrong. It assumes some standard to which our lives ought to conform. Both of these reasons go against the modern trend in our culture which views morality as a matter of private opinion.
Source: Richard Bauckham, n.d. 2 pages.