With regard to moral philosophy (or any philosophy) being called “science”, this is an ancient term (e.g. Aristotle) that was applied to the pursuit of knowledge generally. Aristotle’s metaphysics and ethics were considered as much science as his physics and his zoological pursuits. There was not then the split between philosophy and the “physical sciences”.
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Within the framework of a virtue-ethics in which eudaimonia—which I will translate as “flourishing well-being” (each of those terms is sometimes used to translate it, as sometimes “happiness” is as well; there is disagreement among philosophers as to the best translation)—is the ultimate good, being that which is not instrumental in the pursuit of any further good. For Aristotle, reason was the essential human faculty, but that did not lead him any reasoned rule-based ethics (or to dismiss other human faculties). Reason informs emotional responses and what we might call intuition, as well as our response to cultural norms.
I think that emotions have served a survival function in human evolution, both socially and individually, and are not strictly individual-idiosyncratic. Anger and fear, for example, are linked to the survival response to imminent danger (though they may be displaced). Children who are raised together at young ages have a tendency to feel disgust at the thought of incest, as another (disgust may also be linked to the vomit-response at eating poisonous foods). Joy is experienced in a state of well-being; other emotions signal some ill-being. (I really don't know anything about evolutionary psychology; I am drawing at least a bit from Antonio Demasio's research here, as I recall from reading.)
To have served such a survival function, emotional responses did not have to operate infallibly—only well-enough to support the survival of the species.
Epicurus held that the physical senses were always accurate, but that our identification of the source, our interpretation and our response could be in error (e.g., the picture in our brain may be accurate; it is our—perhaps reflexive—interpretation that leads us to be fooled by a mirage). I’m not convinced that such a strong statement can be made about emotions (I’m not sure that Epicurus’ “always” isn’t too strong with regard to physical sensation as well), but emotions normally do tend to be in response to some (at least potentially) identifiable cause of well- or ill-being. If emotional responses are inappropriately displaced, that too is potentially identifiable.
Appropriate emotional response would be part and parcel of a developed “virtuous character” from a virtue-ethics point of view. (“Virtuous”, here, does not mean “morally” good as opposed to morally evil, or right and wrong, in the conventional sense that we tend to use those terms. What is virtuous is what promotes and supports a generally eudaimonic life.)
When people speak of morality, they often seem to mean some fiat-based, or at least rule-based, system. (Nietzsche seems to have restricted his usage to that sense.) Divine-command morality is a religion-based fiat system.
People also seem to have a tendency to seek some kind of system that will ensure ethical/moral infallibility. I do not think that such a system can be had.
But I do think that virtue-ethics provides a valid framework for the ethical tendency toward eudaimonia, in which both reason and emotions are recognized. When human beings live in association (family, clan, community, society), then the individual’s eudaimonia cannot be pursued in isolation. The individual’s flourishing and well-being are enhanced or diminished by social behaviors and conditions that affect others’ eudaimonia. That may lead to social rules (and taboos) that are aimed at creating the greatest eudaimonic potential for the group’s members. But, such rules should then always be tested against that end, and not allowed to become simply a fiat-based system. Unfortunately, that seems often to happen.
I’m not a utopian. As I say, I don’t think that an infallible ethical system can be had. But, just as emotions do not have to be infallible to serve a valid function for the organism, an ethical system does not have to be infallible to be valid in application. I am not really that systematic, and I borrow from different ethical approaches. (I borrow from both Epicurus and the Stoics, for example, as well as virtue-ethics, as well as the likes of Chuang Tzu.)
In the end, I do think that philosophy has some valid, well-reasoned things to say about ethics. (I’m not a philosopher: I’m just a schlock who studies this stuff on my own, in the interest of my own eudaimonia.) This post reflects no more than where my thinking tends to be on the question at the present time.