I Googled with the phrase "the right to justify their sin" and got 43 hits.

Lyrics copied from http://crossring.com/articles/manik1.asp.html –
With additional lyrics copied from http://livingquest.blogspot.com/2004_08_01_livingquest_archive.html

THIS LITTLE CHILD
Scott-Wesley Brown

1. Who would have thought that long ago, so very far away,
A little child would be born and in a manger laid?
And who would have thought this little child was born the king of kings
The son of just a carpenter but for whom the angels sing?
And who would have thought that as he grew and with other children played,
This child with whom they laughed and sang would die for them some day?
And who would have thought this little child could make the blind man see,
Feed the hungry, make rich the poor, and set the sinner free?
Oh, who would have thought this little child was who the prophets said
Would take away the sins of men and rise up from the dead?

CHORUS: And I believe and I will always sing
This little child is the king.
Oh, I believe and I will always sing
This little child he is the king of kings.

2. Many years have come and gone yet this world remains the same.
Empires have been built and fallen. Only time has made a change.
Nation against nation, brother against brother,
Men so filled with hatred, killing one another,
And over half the world is starving while our banner of decency is torn,
Debating over disarmament, killing children before they're born,
And fools who march to win the right to justify their sin.
Oh, every nation that has fallen has fallen from within.
Yet in the midst of this darkness, there is a hope, a light that burns.
This little child, the king of kings, some day will return.

3. Who would have thought this little child is who the prophets said
Will return to judge this world, the living, and the dead?
Oh, can't you see that long ago, so very far away,
This little child, our only hope, was born a king that day?
And can't you see that here and now as unto him we pray,
This lord of lords who is our hope is still king today?
He's still the king today.

[Recorded by Scott-Wesley Brown and by Katrina Rae.
[This song is even on a couple of Chrismas albums!]