An unconditional ought statement would be one in which the protasis (or the implied protasis) is not a real option and the apodosis does not admit of circumstances which change the nature of the act. The protasis (stated or implied) that tends to govern such unconditional ought statements is “If you want to live a good life” or some such like. The phrase “if you want to live a good life” does not really give you an option. You do want to live a good life–regardless of how you define what it is to live a good life–because the good is that which both is and is desirable, or alternatively, that for the sake of which, or that which all men seek. Obviously I’m summarizing a lot and cutting out many excellent debates about the meaning of “good,” but I hope you see where I’m going here.
This is an excellent quick summary of the concept. However, as you correctly note, this concept rests upon the idea that the “good life” is something known and agreed upon, which is far from certain.
I tend to be of the opinion that all “ought” statements are conditional. For example, you
ought to be kind but people, but only “if you want to reasonably expect people to be kind to you in return” or “if you want to make friends.” If you don’t want either of those two things, you’re under no obligation to be kind to people. Now, as it so happens, most people
do want to make friends and want to expect others to be nice to them. So as a kind of quick shorthand, it’s acceptable to say, “You ought to be nice to people.” But there’s nothing “objective” about the whole thing.
Negative “oughts” only come into play when a person first wants to do something. For example, I never seriously want to steal things, so I don’t need to consider the “oughts” of it. It’s just not something I’m going to do. But let’s say that one day I get an incredible urge to steal something. Then I would have to consider things. I ought not steal…
if I don’t want to risk getting caught, or
if I don’t want to feel bad for the victim of my crime or
if I don’t want to undermine the lawful society that I live in.
If I don’t care about getting caught, if I don’t care about my victim, and if I don’t give two hoots about the lawful society I live in (or, more likely, if I judge that my minor violation of the law won’t make that much of a difference), then there’s nothing to stop me from stealing if I really want to. Fortunately, I do care about those things, sufficiently enough to prevent me from acting on my desire to steal if I should ever be struck with such a desire.
And that’s about it.
For other oughts – particularly victimless oughts, like “I ought not engage in homosexual sex” – these things apply only “if I want to follow the moral code of Catholicism,” or something like that. And that raises the question of why I would want to follow such a code in the first place: I don’t think there’s a god, and I don’t think the Catholic church’s teachings have any special significance.