Hanging would be too merciful. What if there is no God and no final judgment ?
Would, say, 30 years in a cushty British gaol watching Sky, working out, eating chips and Sunday roasts be suitable punishment ?
I think some of us could be rather more inventive about the type of punishment we'd mete out - it would be very cheap and only take a couple of weeks in a disused farm house.
And the same for the bastards who stabbed an innocent 17 year-old lad to death on his doorstep (and set about his parents with knives while they tried to administer first aid to their poor son.)