That doesn't break it though does it , in this case in your scenario you'd hang mercer who is currently still in prison . The rest wouldn't be executed because they weren't convicted of murder.
Not to answer for somebody else but I think the point the poster was trying to make or rather the point i'd made is that it's about more than one despicable creature shooting an innocent child , it's about young men across a community many of whom will never commit murder but that doesn't mean they don't present a problem to society, so trying to prevent their behaviour escalating to murder or let's be honest to any serious offending has to be better than a child dying and then executing somebody. I'm perfectly happy for mercer to be in prison forever but that only solves the mercer problem it doesn't solve the problem of the other youngsters who might grow up to be mercer and the impact their behaviour has across society on both a personal and even a financial level .
I'm not saying everybody on every estate is bad news they aren't , there are loads of great people let's face it we are them, we know them and many grow up to do really good things . Any attempts to tackle issues like this though have to have multiple approaches. if you have a leak you don't just mop up the water and leave it , you have to find the cause of the problem and stop it happening again . Or at least try , surely ?