In UK for centuries the Death Penalty pertained for scores of crimes, some quite petty such as small thefts. Never did any of these hangings, some of small children (in public until 1868) deter people from committing crime, as the crime rate remained steady right through. I can't imagine a violent bank robber, for example, putting his gun back in his pocket and saying to himself "I'd better not use this, I might be hanged!" If we reinstated public hangings, we'd be regressing to primitive times, and imitating the gruesome and uncivilised executions carried out today in various parts of the world eg China, Saudi Arabia, and other fundamentalist states. Would that be progress??