Dervel this is only indirectly relevant to the original topic of the thread, but I would like to respond -- in any case, direct engagement seems more-or-less played-out by now.
So, anyway, I would like to advocate a rather more optimistic view of secular ethics than you express.
As you say, Dervel, ' there is no rational proof for secular ethics '. This might seem less of a problem, though, if we consider (which is true) that there is likewise no rational proof for ( secular !) physics ... or even for what has often seemed the epitome of certain knowledge, mathematics.
Standard axioms for maths (Zermelo-Frankael or equivalent, say, with or without the Axiom of Choice) admit of no 'rational proof'. Do we, should we, then worry about maths being 'merely subjective' in the way some people worry about morality and ethics being so? Is maths culturally subjective? Well, possibly, in a way, yes of course, it has to be. How big a problem is this, though?
Fine, there is in fact less disagreement about maths than there is about morality. But turn this around: the existence of disagreement entails at least an assumption of there being a right and wrong. Remember ' de gustibus non disputandum ' -- there is no (there cannot be) argument about taste; morality is not just a matter of taste.
More: your reference to religion allowing a basis for morals lacking in secular thought, although very much a 20th century theme (in Nietzsche, for instance), is not as clear cut as it might seem. OK, I know some Nietzsche scholars and acolytes sometimes throw a bone or two to the dogs of Divine Command Theory, but really we all should have had second thoughts about religion supplying objectivity to ethics and morality at least since Plato's challenge in the Euthyphro. (A search on 'Euthyphro dilemma' will fill in here -- choose your source carefully!)
This is all either too much or not enough. I did want to suggest, though, Dervel, regarding your pessimism about secular ethics and morality, and associated problems around objectivity and reasons, that such pessimism is misplaced.
Derek Parfit wrote, in epitaph to his Reasons and Persons,
Non-Religious Ethics is at a very early stage. We cannot yet predict whether, as in Mathematics, we will all reach agreement. Since we cannot know how Ethics will develop, it is not irrational to have high hopes.
This is not to say moral questions are easy. But, look: read, those who have not already, Judith Jarvis Thompson, A Defense of Abortion. Engage with her arguments; consider whether your man Hunt is likely to have done anything similar at all; wonder why such a person as Hunt expresses the opinions he does. Then ask yourself, 'Did I need " a rational proof for secular ethics " to do any of this?'