Morality

[The Grand Nudger]

You're under no obligation to watch total drama island.

No shit, lol!

In platonic moral realism moral facts and moral obligations are not distinct subjects.

So?  In reality, they are.  That's always the problem with idealism, huh..lol?

In fact in order to be moral anything, the obligation, the ought has to be a part of it.

Not so much.  What you're discussing is deontological ethics.  

Holocaust is morally wrong. I'm assuming you accept this as a moral fact?

I do, yeah.

Now explain why this is morally wrong, without reference to obligations, or oughts.

Harm.

Is it just a description of the negative societal impact of the holocaust? Or something akin to such explanations?

Could be, sure.  When we refer to negative societal impacts we're referring to conceptual harm..but it's sheer presence doesn't compel us to avoid it, and we may have good reason to do that harm (or to let it be done) - so..you can see, that no specific obligation presents itself at this point or level of scrutiny.  

We require an evaluative premise -in addition- to our moral fact, in order to derive an ought.  This is what the much bandied around is-ought problem refers to.  It's the addition of the evaluative premise that supplies the ought, not the mere existence of the moral fact (in this case, the harm of holocaust).

We could run the same in reverse, btw. We could posit that holocaust is morally good, or we could posit that holocaust will benefit our society. Neither of these things, by themselves, is a compulsion to holocaust. We'd need the addition of a different evaluative premise. We obviously don't do everything that's good, or that will benefit us...the situation is identical no matter which direction you take something (and regardless..again, of morality's ontological status).

In either case, generalized, we'd need some premise along the lines of "we should always do whats good, or whats good for our society/we should never do whats bad, or whats bad for our society". Neither of these things qualifies as a moral fact in a realists conception. The specific nature of obligation (it's limits) and how we determine the consequence or reward of success or failure in obligation is actually a big deal in contemporary moral realism. It forms a sort of trifecta of related but distinct subjects.

The moral schema.
Purported obligations.
Coherent consequence.

Morality, deontology, desert.