The point is that even today, subjectivists are rationally forced to conclude that slavery was also right, on the basis that the slave owners believed it was right. Indeed, since their whole society and whole half of the US thought it was right, even the subjectivist who tries to appeal to group-belief has to think slavery was right.
Subjective morality would mean that there is no ONE morality, you keep treating subjective morality as though it needs to operate in the same way objective morality would.
The individual chooses what is moral/immoral based on their value structure and creates their morality, which is not held by others. Similarities exist due to similarities in nature and nurture from person to person.
They have zero rational warrant for doing it. As you say, these people are "dictators," to use your word. They "dictate" to others what they can and cannot do, without one hint of actual rational authority for doing it.
That's moral subjectivism. Power rules. Rationality in moral matters is framed by them as impossible because, as they say, there are no facts about morality.
That's how morality works, it is enforced using power. You can try to persuade others to your point of view but ultimately morality includes your ideas about how others should behave and while you aren't required to exert your ideas on others, morality would be pretty pointless as a concept if you didn't.
I know that in your world, subjectivity simply means preference, but I haven't decided that morality is subjective just because I wanted it to be. I can't ignore inconvenient truths and pretend things are what they aren't, that's the same as just sticking your head in the sand and hoping all goes well.
You don't know if it's wrong. You think it's wrong, maybe. And you want it to be wrong, maybe. But you have no way of knowing for sure that you're right, if you're a moral subjectivist.
For a subjectivist, the "mature" view might still be that slavery is right. Who defines "mature," in a subjectivist world?
That's a good reason for questioning moral subjectivism, isn't it?
If morality is subjective, then slavery can only be thought to be wrong as there is no such thing as a thing being objectively right or wrong. That is the entire basis for the understanding. Mature is similarly determined by individuals, groups and organisations and alternative definitions compete for usage as culture and society advance.
You think a good reason for questioning moral subjectivism is that it's inconvenient but I don't share your view.
It's kind of silly that this far into the conversation, you don't appear to have even the most basic understanding of what morality looks like in a subjective morality framework. You don't even appear to understand what subjectivity is, mistaking it with preference constantly and refusing to be corrected.
I don't see any reason to continue this conversation, I will excuse myself from it.
@ Peterholmes
I mostly agree with your summary of our position, although I never made an argument that viewing morality as objective would bring superior results - I acknowledge that a very good argument can be made for it which shouldn't be taken lightly. It mostly comes down to what degree people can assert their value structure as being meaningful and worthwhile.
Nice talking with you.