[With all due apologies to those who have done all that homework for their philosophy degree...you are about to see why I envy your accomplishment.]
Life is precious. Agreement on that sentiment is so nearly universal it is not often spoken of as a belief or treated as an arguable proposition. But strictly speaking, that life is precious is a belief and there are some: philosophers, the terminally ill, depressives, etc, who will question it or put conditions on it. Many are able to understand that principle on all its scales: the longevity of the individual, of a species or of a community of interdependent species is almost always held to be something worth prolonging.
But in this world, living as humans do, we promptly fold, spindle and mutilate even that simplest notion of a good thing into a knot about which there is persistent disagreement:
When is it permitted to take a life?
This is a wicked hard question. Simplify it ruthlessly. Leave out the other species, even those that have done us no harm. Leave out any whose status as "living" is in question. Leave out all who have tired of their burdensome existance. Leave out accidents. Leave out Gary Gilmore.
[what! You thought I'd never get around to him?]. We are now down to ending the life of a person, conscious of life and death, who would prefer to continue living. Considering when it is acceptable to take a life in this narrow scope is still a terrible question to ponder. One million shades of gray still reamain for our discernment. Well, I am not about to write a pocket guide to replace millenia of judgment on so heavy a matter and you wouldn't read it anyway. What I do mean to illustrate is that there is a way to start from a point where common sense and common theology are still in agreement and wind up at some reasonable guidance without requiring or rejecting the text of any particular sect. [Thats how I spell progressive, dear reader: maintaining the hard-learned rules that would come closest to accommodating every member of society...just as they are]
Let's keep whittling: Self defense, capital punishment, waging war, too many mouths to feed and others are all yet on the table. War, to turn Von Clausewitz slightly on his head, is failed politics...I leave it out for the sake of brevity and because politics should be fixed before wars happen...another way to spell progressive. I don't consider myself well informed about capital punishment and instead offer you this until I am read up:
Life is precious. We say so meaning that we would try to protect not just our own life but others as well. Since when is vengence or punishment precious?
My purpose being illustration, let me just pick one instance from the sagging shelf of justifiable homicide: Self defense. That is a knot. Life against life, take a life to save a life. What tips this balance? Here is how I work this out using only what I consider common sense. I apply the basic idea that life is to be spared while resisting a long as possible the selfish and blinding thought that some lives are more precious than others. I strive for practical judgement: what works best, what difference will the choices make? In general then, the fewest lives lost in the long run is a good basic goal. It is close to impossible to accurately project yourself into the life and death situations I will now categorize, though we inaccurately do so constantly thanks to lurid quality of local news. When the debris of these situations is put before our judgement, we are called upon to put ourselves in the place of the accused. Note that I describe these situations from the view of the person attacked.
First eliminate the unnecessary risk of taking life by seeking an outcome where no life is lost. Is escape an option? Could buying time help: will this assailant hunt me or am I just momentarily inconvenient or the object of a passing rage? If I have been party to provoking this hostility, my pride is a trifling thing and I should try to diffuse the situation. If physical restraint and deadly force are both possible, favor restraint: be the human where no one else will be. I don't know much about crime stats or criminal psychology but the presence of mind to run through those possibilties in the moment would save at least a few lives. "Stand your ground" legislation goes in the opposite direction. I hope such laws, if enacted, go under the microscope of well kept crime statistics. I expect the difference such laws will make will be how many more "lie in the ground".
When no peaceful option is available, our arithmetic increases from zero to one. You face an implacable personal foe. You are cornered, no one else is theatened. One is full of anger the other full of fear. I gather much domestic violence fits this case, the common tragedy of the unstable nucleus of the atomic family. What works best? I don't know. This is just sad and life gets wasted. All the ethics in the world are elsewhere and will come around later to mop up the blood. All the cases are particular. But if its just a fight, a slight hope of it being less than a fight to the death hangs on one of the combatants dropping pure anger for pure awareness...just try to be that combatant.
Reckoning lives taken is certain. Saving lives is the greatest good our civilization can manage but reckoning lives saved is speculation. That should temper how we think about the attacker with many targets and especially targets in the future for we only guess when we say "he'll kill again". But when the arithmetic must balance the lives of more than one victim against the one life of an attacker who has the means and the history to do fatal harm, the only question I would have is whether killing the attacker is the only option. Always: life is precious. So more lives are more precious.
There you have it, a worked ethical exercise, neither scholarly, religious nor complete and perhaps a strawman of an exercise. I make no pretense of stumbling through such reasonigs in a vacuum and inventing answers: I grew up in a culture where law and custom have long traced many shared ideas that life is precious back to Judeo-Chrstian teachings. But neither would I buy anyone's pretense that those traditions have all the answers: I know many Jews and Christians, long confirmed in their faith and usually unified by it, yet falling out into a spectrum of opinions on issues like capital punishment. They are just people who have taken the guidance they received and reached their own conclusions. The main point I try to make here is that one can start from really basic and generally held values, advance by applying the practical constraint that extrapolations must make a positive difference for as many as possible and arrive at rules of guidance and judgement that could be used with benefit in particualar, even extreme, real life situations.
One other point of my discursion is that having labeled myself as progressive does not give anyone reason to label or attack me as opposing their religion and particularly not to claim I have no values or values antithetical to Judeo-Christian morality. It would be hard to say a progressive was a person with this or that particular issue or belief. It would be safer to say what progressives are not: they are not people who throw out the ethical baby with the mythical bath water. In my case at least, being progessive means I want to clean the baby we must all care for of any self serving myths so that one day, it will take care of all of us.
In the end justice is simple regardless what complexities accompany its attainment. Its simplicity is this: say all parties are equal, say today counts as much as seven generations hence but much more than yesterday and with the scales thus set, be practical. Try to make the balance of life work for all that live. If you feel you have a maker, do you imagine he wants things otherwise?
I admit, I have glossed over all the hot buttons; abortion, mindless life support, and of course capital punishment. When I have time and need attention enough to invite getting kicked around, I will tackle those using my farmboy methods...later.