Well I am sorry to say that I am too stupid to know what meta-ethical moral relativism is, if it applies or does not. All I can do is try as best I can to speak using words, you hopefully know, that clarify what I feel, so, I can't comment on whether we are destined to agree or disagree.
What I can perhaps do is tell you how I feel about the rest of your words. I have no problem with 2+2=4, however the fact that it's four and we can agree on that doesn't tell me we know anything that is relevant to the situation we are discussing here. Some of us here seem to want to assert that our feelings about buckshot have a mathematical precision and I am saying that unlike 2+2=4, which evokes no triggered emotional response, the reactions to buckshot are chock full of them. I am saying also that where those feelings are unrecognized, suppressed, for example, they introduce unconscious bias. Anytime something is suppressed that is hidden behind some sort of intellectually created structure, so ethical, moral believe, there arises a need to defend it, a fear it will fall, and a terror of what is suppressed will surface. If that's meta -ethical moral relativism then I'm in.
Note also that even when one may be on the right track one can be on it for the wrong reasons.
What I have done is conclude that I do not know where buckshot is coming from. I am also neither educationally qualified to argue esoteric out in the weeds notions of it, and don't have the time or the interest or likely the talent to acquire such information, but I also have full faith that whatever the truth is it will out or has already has. I hold the consensus view without any need or terror of being right or wrong and am thus unable to generate the outrage so many do here toward him. But I can say that all the kerfuffle he generates tells me there's a dead rat hiding somewhere. I call that kind of rat ego attachment, unexamined assumptions that require rationalizations of one kind or another to stay suppressed.