'Is & Ought' in David Hume

[Mudhammam]

The first thing I want to say is that you are going on to another topic, which is, what is the basis for morality?  I would rather have that discussion in another thread, and keep this one about the question of whether moral principles can be derived from matters of fact, and what Hume had to say about that.

(bold mine)
I guess I'm not entirely sure how it is that you conceive of those distinctions as entirely separate... Isn't the question as to whether a well-reasoned survey of the facts can suffice in conferring moral duties or principles another side of the same coin, as to where precisely lies the basis for moral duties or principles, viz. in establishing their ontological ground?

Your hypothetical is a practical matter, rather than a matter of morality.  To borrow an expression from Kant, you have a hypothetical imperative, not something that applies categorically to everyone.  Whenever you have an 'if-then' kind of statement, a hypothetical statement, it only applies to those for whom the antecedent is relevant.  To illustrate how this sort of statement is not providing moral guidance, consider the following example:

If you want to molest little children, then you ought to say things like, "hey little girl, want some candy?" to lure them in.

This is all about means to ends, and does not provide an end; the end is presupposed (in the antecedent, the part connected to the 'if' in the sentence).  And it is something to be ignored by anyone who does not have any interest in the antecedent.  Notice, this is not something that is about morality, but about achieving a particular goal.

I agree that conditionals only apply to those of whom the antecedent is relevant, but I suspect that there are broad enough conceptions of happiness or well-being that do necessarily apply to all with a capacity to think and feel. That was the point of my preceding syllogism, that every human being, on account of sentience and rationality, have some interest in their own well-being, even if their opinion of what that translates into as a practical matter is so utterly wrong that their notion of happiness and how to best achieve it results in outcomes that are highly destructive and/or counter-productive to greater states of happiness. I don't see how morality could be about anything other than achieving a particular goal, i.e. happiness, though on account of the human condition this is a goal that every person shares (with varying opinions as to the correct definition or expectation of what this should be like in actuality).

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But doesn't your "one ought not to kick babies" amount to a disposition one would want to instill in their kids?  What good is it to say that to an adult who has just kicked a baby?  Apparently their parents failed.

I think you're trying to define morality too strictly in cognitive terms.  We can articulate what we feel is moral and in the vast majority of cases we'd find agreement.  Does that mean morality is an empirical matter to be determined through polling?

Sure, I do think morality is an empirical matter, and in terms of judging whether a person has lived a virtuous life, that it is to be determined by examining those who appear to live the most productive and satisfying lives, and not simply according to their own view of themselves, but also through polling those effected by their actions or inaction.