Objective morality: how would it affect your judgement/actions?

[The Grand Nudger]

So for example, if we were somehow magically given factual information that "putting someone in solitary confinement is not wrong", then that would mean all the things we thought were harmful about it are somehow not as important as we thought; or else, there are some sort of countering benefits that cancel it out that we're unaware of.

You've got it backwards there, in a harm based moral realism.  We could conceptually receive factual information that tells us that solitary is not harmful, or not harmful in the manner it was supposed to be, and that would be why it would no longer be considered immoral to put people in solitary for that reason.   

My point is that no one would act on this "fact". We'd retain our way of doing things. We would surely do more study, to try and understand why this "fact" is the way it is. We'd try and uncover potential hidden benefits, or consider the way we look at "harm". Not until we understand why the fact said what it says would we act on it. Yet it must be "correct", by definition. This is the contradiction I'm presenting.

Why do you suppose that?  Yes, I understand that there's a strong trend of conservatism in all things..but, it seems to me that we do act on new information thaty some x isn;t harmful, and change our ways of doing things.  We once thought it would be harmful if women could vote, lol.

What I'm trying to say is that there is no single correct way of determining "harm" or "benefits", so the idea that there can be facts about them doesn't make sense.

Having more than one way to determine harm and benefit is greatly useful to moral realism, it's not something that makes it incoherent.  If you wanted to make factual statements, you'd want as many tools as possible that could determine either. Whenever I do a site survey, I carry all sorts of shit with me. I expect that you have alot of career specific apps and tools that you use, as well.