Sin, Mercy, and Justice are the trinity of the human mind. We worship, as Catholics, the Trinity of God the Father, God the Son, God the Spirit. But we act in a fallen mortal world- a world where Original Sin is a scientifically proven fact by preponderance of evidence (ok, the science is theology, and since a few atheists follow me, I'm sure they will disagree with that, but I'd ask them before they jump on that if they've ever acted against personal conscience- doing something they knew was wrong and justifying it afterwards). And where there is sin, there is need for mercy. Where there is mercy, there is also a need for justice. These three concepts are so intertwined that (with apologies to Kasper the friendly Cardinal, who I know believes differently) they cannot and should never be separated.
Luke 17:1-10 tells us that we should forgive the repentant. But what are the repentant, if not those who seek to do something to repair the temporal effects of their sin, who seek justice for their own crimes? And are not these the very people who deserve mercy the most?
Likewise, the man who seeks to avoid his sin, who claims that it is not sin, and who does no repentance- has not done justice. And thus, does not deserve mercy.
Using the Year of Mercy Logo above- which I detest, but does include this point- it is not only Christ trying to see through the sinner's eye. It is also the Sinner trying to see through Christ's eye. I know many liberal evangelicals and less than orthodox Catholics who only see the first- and forget the second.