There are no definitive answers to this question I'm afraid, merely opinions ... but it's good to see some people's opinions bearing in mind we will all come at this from vastly differing angles ... angles such as religious, moral and legal, all serve to confuse, none of which succeeding in totally clarifying.
It's easy to acknowledge the number crunch of a thousand deaths to one but it comes at the expense of breaking one of life's fundamental rules, murder.
To kill another human is an immoral act and goes against every form of humanity you care to reference.
As long as you can square that circle of the conflicting morality, legality and maybe religious agendas, you will have no problem in pulling that trigger.
Factor in all of the differing agendas society reflects and you have the recipe for a question that can never be answered definitively.
Have fun