Should we expect Christians to live differently?

Luther said that "Life is as evil among us as among the papists" (p. 57, Heiko Oberman, Luther: Man between God and the Devil).

Tim Keller who is deeply influenced by Luther's radical doctrine of grace often says the same kind of thing. e.g:

It is often the case that people whose lives have been harder and who are "lower on the character scale" are more likely to recognize their need for God and turn to Christianity. So we should expect that many Christians' lives would not compare well to those of the nonreligious (just as the health of people in the hospital is comparatively worse that people visiting museums).

(p.54, Reason for God)

In a similar vein Alister McGrath says that he sometimes would respond to comments that "Christianity cannot be true because I know X and he is a horrible person" by saying "just imagine how much more horrible X would be if he wasn't a Christian".

I don't quite understand how to hold this together with the teaching of 1 John and the like. I often feel the NT does lead us to expect that Christian's lives should compare well with non-Christians. But maybe my trouble is I'm confusing 'should' with 'will' instead of 'ought to'.

I 'should' read Luther on 1 John, but unfortunately it involves £20 outlay.