Often in our divided world we disagree with someone about a principle.
Person A says that what matters is reproductive freedom and B says that what matters is protecting the unborn. Person C says that what matters is protecting American security and D says that what matters is hospitality to refugees from tortured lands.
Principles conflict and we can't agree on what's right. That's one kind of argument. It usually doesn't get very far, because if we disagree on principles we often find ourselves in a deadlock rather quickly.
But sometimes we actually agree on principles while still disagreeing on how best to put them into practice.
Person E says that what matters is compassion to the poor — very happily, F agrees. But F thinks compassionate care for the poor is best handled by the church, and E envisions a greater role for government.
Or, both E and F agree on compassion toward the poor, and on the church's central role. But then they discover that they disagree about the best way to implement such compassion. E believes in spending the church's resources on a targeted program to house a small number of homeless people, while F would rather offer free lunches each day at church to a larger number of people.
Or perhaps E and F agree on compassion, and on the respective roles of government vs. church, and on a massive free lunch program at church, but disagree on whether people should be able to get food every day or only every week, or who is responsible for providing the food, or whether people should be allowed to camp out in front of the church before and after getting their food, or ....
You get the point.
Let's follow a move mainly made in Catholic moral theology and call this a distinction between judgments of principle and prudential judgments.
People can agree strongly on a moral principle but disagree strongly on the best way to advance it. The latter is a prudential judgment rather than a judgment of principle. It is sometimes mistaken for a judgment of principle, however. E concludes that F is not adequately compassionate, but instead F has concluded that the best practice of the principle of compassion just looks different from what E thought it should look like.
When this happens, mutual incomprehension and frustration are sometimes worse than if our interlocutors disagree on the principle itself. It is as if they are in the same moral neighborhood, which is great, but they find that just being in the same moral neighborhood hasn't resolved crucial differences of opinion between them. They had not expected this and they find it quite frustrating.
Pope Francis, I believe, is facing exactly this issue in disputes within Catholicism over such issues as the sacramental status of Catholics who have been divorced and remarried, or are in "irregular family situations." He and his critics seem to agree on the key principles but not on how they are best implemented. (At least, that is the pope's perspective on what is at stake.)
It helps to remember that a different kind of moral reasoning process is required with prudential judgments over against judgments of principle.
To arrive at the most important relevant principle in most situations mainly involves resorting to the major norms of the moral tradition you are operating in.
But to arrive at prudential judgments involves analyzing often complex situations, assessing the motivations and behaviors of people under various conditions, judging anticipated outcomes of various courses of action, weighing costs and benefits of different approaches, and so on.
Prudential judgments are best performed by people who have the relevant expertise and experience with the concrete issues at hand. It is a conversation about practical wisdom in relation to important goals but complex human realities. It also involves accessing that elusive realm called the "factual," or that even more elusive realm in which facts are projected for the future based on key assumptions and experiences from the past.
A sports analogy comes to mind. In sports the goal is to win, and the main operative principle is to do what it takes to win, within the rules of the sport. But that just leaves open a hundred different prudential judgments about what to do during any particular game situation in order to win. Blitz or no blitz? Run or pass? Punt or go for it on fourth down? And so on.
If you are morally passionate about a specific principle that you consider nonnegotiable, that's great. But do not assume that even those who agree with you about that principle will agree with you about the best way to implement it in a particular set of circumstances. Agreement on the principle, if you can get that far, is the beginning rather than the end of the conversation.