The purpose of hanging him is not to show that he is wrong.
It is to set an example.
It tells people: "You bring drugs in I don't care what story you tell me you are going to die."
The result of this is almost nobody ever brings drugs in, because there is 100% no chance of leniency.
Some countries prefer to do: "You bring drugs in ah, ok what's your story?"
The result of this is some people will try luck and bring drugs in because they know there is a chance they might get away.
Where you want the balance to lie between compassion vs safe streets will decide which country you enjoy living in.
"To anyone who still believes that Nguyen Tuong Van deserves to die for drug trafficking, wake up to your hypocrisy." -Shayne Chester
I don't think this is the crux of the issue. In Singapore, our laws protect society over self. The important thing is, he brought in drugs. So "what message do we want to send out to people, for the greater good of society?" Not "What punishment does he deserve?"
A) We are compassionate, you may try your luck bringing in drugs.
B) We are stern as hell and barbaric, don't you ever try bringing in drugs.
No wrong no right, every country has their own policy. Does he deserve it? Maybe not, maybe yes. But hanging him sure as hell will keep a lot of potential drug dealers out of Singapore.