maybe moral progress is in the same camp as scientific progress in a stumbling march through history towards something objectively true.

First you need to prove that we are objectively progressing morally- slavery still exists today (including but not limited to sweatshops), and gay people have had rights in some old tribes and communities. So I don't know if this is universal progress, or still just subjective. Yes, I think societies with gay rights are better, but I don't know of I can say that objectively.

Anyway, that's beside the point. Let's accept your argument that we are matching towards moral truth. You also need to make clear the basis of this objective morality we are matching towards. That's the question at hand. Is the basis of this subjective or objective? Is it understanding the reality of the universe? No, the universe is cruel , and inefficient. So, what have we based this objective morality on. What is the truth we are striving towards?

Science is different because we're understanding reality, and we are able to do things based on that. But what reality are we basing our morality on?