but morality is so circumstantial, and there are some things that are just so intrinsically ambiguous that there are in fact no indisputable ways, besides consensus, to determine morality for them.
The point of morality isn't to have an absolute, perfect sense of what is good and not. The point of morality is to try and understand what people need, why they need it and the consequences of our actions so that we can make better decisions. Consensus has nothing to do with that understanding, but sympathy, empathy and observation do.
Morality can indeed be circumstantial. The same action in two different circumstances can have vastly different consequences.
Ethics though are a different matter. Ethics is the study of what we owe one another. Where morality (what people need and how my actions affect that) is circumstantial, ethics shouldn't be. If I owe people truth or dignity then I always owe it to them, regardless of whether I think they actually need it today. If I don't supply you with truth or dignity today then that's entirely a reflection on my ethical character, and not on your worth.
Reflection is a valuable ajdunct to developing a moral and ethical sense. What others see helps to add to our stock of knowledge. But I believe that consensus is useless, except in shaping custom. Consensus produces harm and inequity all the time -- all that's needed for consensus to be amoral is for a majority of people to be blind to their consequences or unconcerned for their impacts (which I think is often). All that's needed for consensus to be unethical is for a majority of people to reach agreement based on what's convenient for them (which I think is often).
What consensus produces is custom, and custom is frequently used as a substitute for morality and ethics. Custom doesn't necessarily produce good or equitable outcomes but it does at least operate predictably, which is perhaps why some prefer it. People tend not to criticise us if we conform to custom, even if what we do is harmful and inequitable.
It may sound from the above that I'm saying that morality and ethics are personal and subjective. I'm not. People who are sincere about making better decisions based on real evidence will tend to come to the same decisions because empathy, sympathy, sharing observations and mutual reflection will take them there. That direction may be a different direction to custom though, depending on whether we're observing and reflecting, or just bowing to social norms.