The position we have arrived at is this: in defending a moral theory, we must see how well that theory fits in with a wide variety of judgments that we are inclined to make about many different matters. We have opinions about cases, about principles, about the nature of morality, about what counts as an adequate explanation, and more. Some of these opinions are fairly specific, others are more general; some are arrived at rather "intuitively" and spontaneously, others only after considerable reflection; some are extremely difficult to give up, others are more easily abandoned. We try to find the moral theory that provides the overall fit with this eclectic set of beliefs. But if — as seems overwhelmingly likely — no theory can actually accomodate all of the relevant initial beliefs, we revise the set: we alter our beliefs, and reevaluate our theories, until we arrive as best we can at a theory that seems on balance to be more plausible than any of its rivals. Ultimately, then, defending a normative theory is a matter of arguing that it provides the best overall fit with our various considered judgments.
If something like this picture is correct, then defending (or attacking) a normative theory will virtually never be an open and shut matter. Almost any normative theory is likely to have its counterintuitive aspects, and people can sincerely disagree as to which theory is, on balance, the most attractive. That is why there are few or no "knockdown" arguments in ethics (or anywhere, for that matter). All you can do is point out the attractive features of your own favored theory, explain why you are prepared to live with its various unattractive features, and try to show that the alternatives are even worse.
What this means is that you will not be able to persuade eveyone of the truth of your position. So be it: you cannot persuade everyone. But that does not relieve you of the obigation to try to defend your moral views, and to revise them if you cannot. For each of us must decide how to live, and given the importance of that decision, it behooves us to examine whether our own moral views can indeed be defended.