Devastating news.
However, as you are advocating a political action in response to this serious issue, allow me respond.
Alcohol or drugs are only means by which inhibitions are reduced so our beliefs and attitudes are less likely to be repressed. Even the actual punch is only the physical manifestation of those beliefs and attitudes.
Demonising alcohol and drugs, or even the coward himself, does not address the real issue - which is the underlying beliefs and where they come from.
For those who still struggle to understand how someone can feel the need to express his manliness or power by acting with such utter contempt for a random stranger, I suggest these attitudes stem directly from our social and economic system which rests on the right of the powerful to use their advantages to prosper directly at the expense of others. The more ruthlessly they take their advantage the more successful they will be at attracting greater power and wealth. The start point is that we don't all bargain on a level playing field.
When calling for change, we can advocate for increased State policing, which leads to erosion of civil liberties, and which ultimately is the road to fascism. Or we can demand real equality, where respect for the value of each person is reflected in basic entitlements. For example, the right of every person to a real job on award wages. That is ultimately the path to a real democracy, instead of the token shell of one we currently enjoy.
Of course the forces of capitalism will fight the second choice tooth and nail. They will utilise all the propaganda means (and ultimately all the military might) at their disposal to preserve the right of the powerful few to exploit the rest of the world. We live in a paradise for economic bullies.
Calling for a 'law and order' solution to social issues like these merely obscures the real forces at play.
Moreover, treating the symptom instead of the disease will generally fail to achieve the desired result. A cursory glance at criminological research worldwide will tell you that increased penalties have little to no effect on crime rates.
The despicable coward who killed that young man has no sympathy from me. However, for the above reasons I am opposed to the petition.