Jos Gibbons:

What is "a universal mind"? A god posited as being omnipresent within a universe He created doesn't get to have any less subjective thoughts than any other mind.

Universal mind = omnipresent, omniscient. A god whose thoughts are subjective isn't compatible with the typical conception of God believed by monotheists. Given that another of God's supposed attributes is omnibenevolence, how could his thoughts on morality be subjective? If there were no moral truths it wouldn't possible for moral perfection to be part of God's nature, therefore moral truths are part and parcel of the theistic worldview - given the common definition of "God".

A Platonic realm's existence is independent of the theistic question. In any case, what about a Platonic realm makes it more plausible it could contain moral truths? The argument boils down to "pretty much anything can exist in there" - which seems to be taken as a defining characteristic of a Platonic realm. You might as well claim this is a morality realm.

I didn't equate Platonism with Theism, but they are both examples of worldviews that typically entail objective moral truths. In the Platonist view, moral truth (The Good) exists in the Platonic realm along with other abtract universals such as ideals of Mercy, Virtue, Beauty and so on because universals are what the Platonic realm contains, by definition. Its existence is independent of the theistic question if we are talking about a big-tent atheism, but it is not compatible with Dawkins-style materialist/naturalist atheism.

Platonism and Theism (with few exceptions) assume the existence of moral truths, implicit to their worldviews. Naturalism doesn't.

For statements about what is ethical to do with private property to be true, we only need private property to exist. As far as I'm concerned, it does. It may only do so by decree, but that doesn't mean it doesn't exist, only that it otherwise wouldn't.

No its not enough, because declaring something ones private property is itself a moral claim, it's not simply a concrete fact of existence that we can acknowledge and then ask how it is ethical to treat it. For example, a central principle of libertarianism is self-ownership, and that this ownership is recognized, as opposed to granted by a sovereign power. For this claim to be true, private property needs not only to exist, it needs to exist independently of external decree. To say it exists by decree is abandoning morality in favour of some kind of legal positivism. Other basic human rights are similar.

Replace utilitarianism with X in that sentence, and you have something that's true of any X - so why did you single out utilitarianism and the occasional other thing as the only Xs you won't let the criterion use?

No, you can't replace it with any X, for the sentence to make sense you can only replace it with other Xs that are sets of moral axioms, which is what makes utilitarian criteria unacceptable - it introduces circularity to any claim to have found a material basis for morality. You can't derive an ought from an is, so you have to assume a few "oughts" as starting points i.e. axioms. But which to assume? It's ultimately a personal choice, even if you can't choose just any old thing.

If there are several bases on which moral truths exist, in establishing they do one needn't know which of the bases holds, so doesn't need a criterion for one being more plausible than another one.

Different bases will yield different systems of ethics, so we do need a criteria for resolving conflicts when they prescribe different things. If each person or group can have their own "truth" it's not really truth is it?

Talk about an understatement: it wouldn't make any difference.

Some minority definitions of God (Deism etc) might not entail moral truths. So what?

Why DCT's potential introduction of moral truths seems to "count" more for you than utilitarianism would is unclear. It's just a very fancy "because I say so".

Not 100% sure what you mean here but IMHO theism/DCT, Platonism and secular schemes like utilitarianism (if their application is taken to yield moral "facts") are all just ways of trying to magic objective moral truths into existence by saying "let's assume...". There's no reason to believe any of it and every reason to believe moral beliefs are subjective value judgments, or a bunch of special-case behavioural hacks accumulated by evolution that can't be ironed out into a morally-consistent whole.

Explain why moral truths exist more readily on a theistic worldview, then.

Already did that.

But both conventional science and morality also aim to deduce something besides the empirical: in science, explanations; in ethics, assessments.

Hence my qualification "for all practical intents and purposes". Scientific explanations are important, but if two theories both match the data it doesn't really matter for practical purposes which one is used. If two ethical theories give conflicting assessments it does matter, for obvious reasons.

Can you give an example where ethical disagreements remained unresolved for a long time between two theories because neither contradicted itself or known facts?

There is a long-standing disagreement between rules-based ethical systems and utilitarian ones. It is hard to see how any empirical discovery could resolve the dispute, even if utilitarian ethics could be shown to be superior to rules-based ethics in maximizing well-being, as that is a utilitarian criteria: advocates of rules-based ethics advocate following rules/duties even when doing so could increase suffering. For example, consider the question of compulsory organ donation. It's hard to argue against it from a utilitarian point of view, but impossible to reconcile it with libertarian principles of self-ownership and informed consent. Both systems are logically self-consistent and do not contradict any empirical facts.

What makes you think the former wouldn't give us the latter? True, we may have nothing more than well-informed judgements; but scientific theories often make us only well-informed on issues at their frontier.

What makes me think the former (descriptive theories) won't give us the latter (prescriptive morality) is having seen how the ethical theory sausage is actually made. In practise, such theories are loosely informed by empirical data, but they are hardly determined by them with anywhere near the rigour needed to make their conclusions qualify as objective moral facts. The data so grossly underdetermines the theory and has to be papered over by handwaving and judgement calls to such an extent that comparisons to science are tenuous at best.

The utilitarian justification for the prohibition against killing outlined in Practical Ethics by Peter Singer is a good example. One might naively think that after accepting consequentialism and some principle like "minimizing suffering to sentient beings" that it would all just follow nicely, but that's not the case. There are a whole bunch of special cases and objections that need to be taken care of: what about killing someone painlessly in their sleep who has no friends of family to suffer their loss, what about infants with no self-conception and so on, too many to list in detail here, and the definitions and criteria have to be continually tweaked and rejiggled to get the desired conclusions to fall out nicely. It's quite arbitrary at each point whether to simply accept what follows from the axioms as an uncomfortable but logically necessary moral truth, or just change the assumptions to get a more "acceptable" result. For example Singer balks at involuntary euthanasia but ends up concluding that abortion and infanticide are ok, someone with a different set of standards could conclude that an ethical system that condoned infanticide requires some changes to its axioms to fix it.

The lack of progress towards ethical consensus does cast doubt on the ability of science and reason to discern objective moral truths, even if it doesn't prove that moral truths don't exist.

Also I'm frankly amazed that you seem to think that the abortion issue can or has been settled through facts and logic, it's basically exhibit A for moral grey areas and drawing arbitrary lines in the sand.

Why is one of the two premises more important than the other? It's simply a case of p&q-->r.

One premise contains an ought, the other an is, so it's not ought from is, it's just a more specific ought from a more general ought plus a specific is. The moral principle is not empirically determined, only the question of whether it should be applied in a given instance.