I haven't read Molyneux's book on the subject, nor did I watch the above video. I read your post and only wished to comment that, from what I've seen, the only working objective moral system is Divine Command theory.
The following is only based on what I read in this post, so forgive any ignorance: I don't know what Molyneux means by "preferable." Something cannot be objectively preferable, unless established by an objective moral code (but that would be begging the question). Is Molyneux settling for a subjective moral code?
I appreciate Molyneux's political videos, being a libertarian, but I must say that his book "Against the Gods?" contained the worst atheistic arguments I've ever heard—ever. One, I think, was something like, 'gods cannot be eternal because they would die of old age.' Seriously. I expect his atheist moral system wouldn't be much better.