What is the quality of mercy

I felt sad reading about the teen who was arrested after an outburst at a meet the people session. He has low IQ with a medical condition to boot, and got upset after meeting the MP so after walking out of the MP's office with his mother, he hoisted an aluminium foldable chair over his head and slammed it against a glass door. The boy, who has been released on bail, has been told to report back to the police on 12 May, where he may be charged with committing a rash act.

Maybe it is early days yet, but the blogosphere has yet to pick up on this except for Mr Wang (respect!).

I believe Shakespeare said it best in 1596 from his play, the Merchant of Venice:

Portia:
The quality of mercy is not strain'd,
It droppeth as the gentle rain from heaven
Upon the place beneath. It is twice blest:
It blesseth him that gives and him that takes.
The Merchant Of Venice Act 4, scene 1, 180–187

Clearly the teen was wrong in venting his frustration, whatever his IQ is. However, it is also clear that he and his mother need help, and when they sought it, they somehow tripped and fell afoul of the law. Sure, we can prosecute him, but what good would it do? As explained on the internet, only because mercy is voluntary—because it mitigates the compulsions of the literal law—is it true mercy, which drops gently like heaven's rain, a natural and gracious quality rather than a legal one.

Aside from this natural and gracious quality, the bard brings in a religious quality, going on to say (Portia con't):

Though justice be thy plea, consider this,
That in the course of justice we all must see salvation,
We all do pray for mercy
And that same prayer doth teach us all to render the deeds of mercy.

So where is our quality of mercy?