It's a very interesting question and one that I've pondered and read about. If we criticize the Romans (not saying we did), then is that fair? Are we being elitist or cultural elitists? If we take your question to its logical conclusion we would ask is it fair to judge the morals of christians, muslims, sikh, kalahari bushman, people in Spain hundreds of years ago, our own ancestors, slave traders or those who practice genital mutilation and so on. Moral criticism is something I think is challenging yet necessary to go forward. I'll explain that in a moment. We can be accused of ethnocentrism if we ascribe negative evaluations of anyone that is not of the same cultural, religious and moral background as we are. And while I would say that it's necessary to understand the cultural, religious and temporal conditions of those we are criticizing, I would argue it is a necessity of modern society to question their morality. To avoid the cultural relativist or ethnocentric criticism I think we should follow a scientifically determined set of moral determinants. You could criticize me for being ethnocentric but I would argue that cultural relativism has led our modern culture (or at least parts of it) to accept abhorrent things that are amoral.
Let's step back for a second and think about cultural relativism. Is the aboriginal way of knowing equivalent to a modern scientific approach? Dangerous territory as I could be criticized as being racist but I would argue that in many cases (not all) the scientific viewpoint is the correct or answer that is closer to the truth. People fly in airplanes because science is a superior way of knowing. In fact the scientific method is the highest level of epistimelogical development that has been so far developed. Science can make very accurate predictions that no other way of knowing is able to in such abundance. That's not to say science knows everything. That's not to say science understands everything about Bernoulli's Principle for example, but it has achieved a higher level of understanding than any other way of knowing on Earth past or present. So how does this apply to morals or moral criticism you may ask?
Sam Harris in his book The Moral Landscape: How Science Can Determine Human Values, says: "I am arguing that science can, in principle, help us understand what we should do and should want - and, therefore, what other people should do and should want in order to live the best lives possible. My claim is that there are right and wrong answers to moral questions, just as there are right and wrong answers to questions of physics, and such answer may one day fall within reach of the maturing sciences of mind". (p.28) He later goes on to say: "Science simply represents our best effort to understand what is going on in this universe, and the boundary between it and the rest of rational thought cannot always be drawn."(p.29)
Scientific moralism does not currently provide a complete set of commandments if you will but it is so far the foundation of the most complete and most promising direction for such a thing. Let's bring this argument to the question of abortion. The time at which science finds a fetus becomes minimally sentient matters to the moral question of abortions. What is occuring in the brain of the fetus matters. I (as would Harris I'm sure) argue that the unfalsifiable notion of a soul does not matter to the question of the morality of abortion. I would say that a person's material and social support system at the time of pregnancy and the conditions under which that female became pregnant matter as well. Whether the woman will be able to mentally, emotionally and financially look after herself and her baby matters. What would happen to that child if it was given up for adoption in that current time and place also matters when we ascribe the moral valuation of what can and should be done. I am not saying that we currently have a fully complete and easy to follow guide of scientifically guided morals but science can help us make a decision that is on average more moral and over time closer to what the correct decision should be.
Some people say that religiosity is the best way to guide people in making good moral decisions but I strongly disagree with that. I for example do not believe in any god yet I have morals and am considered a decent and caring person. Human behaviour does not become amoral when the 'guidance' of religion is removed. Would you as a believer go ahead and murder someone if you weren't a believer? I don't think so. Religons often provide a ready made answer to some common moral questions but it fails to be something that makes people more moral in general. In fact "research on people's responses to unfamiliar moral dilemmas suggest that religion has no effect on moral judgements that involve weighing harms against benefits (e.g., lives lost vs. lives saved). (from Harris p.146). Science uses evidence and evidential reasoning to come up with answers or at least get us closer to reality. Religion on the other hand is based on faith which makes acceptance without evidence a virtue. Faith is essentially that. The bible is also a book for which we can break down and discount many if not most of it's dictums through the use of science. Many people simply accept the truthfulness of the bible based on faith and their own personal subjective experience. Science has demonstrated the many many ways that our brains are faulty and create memories for example that are simply not true. The bible can provide some fictional stories from which we can possibly make some better or more reasoned moral decisions but it falls far short of a comprehensive guide to morality. The old testament for example has some abhorrent actions taken by a vicious god that we should consider when evaluating it's judgements. Overall the bible is of little value in comparison to modern day philosophy of morality. It's value is in that it can provide some ready made answers for rather lazy thinkers or those who do not have the time or skills to research/learn about science, philosophy, life lessons, morality and love.
Going back to the Roman couple we ask ourself is there one right answer that should be taken? Possibly. But we must also consider that the Roman's did not have access to a scientific moral evaluation scheme. We must also consider the temporal culture, religion and situational conditions they were under. We must try to be empathetic of people's cultural folkways, situation and so on but we should still work towards a more scientific and logical morality. Do I have all of the answers? No. But I would say that with science as my guide I am better off than if I merely accept the fiction of the bible as truth. I am more willing to accept the scientific understanding of creation for example than a first nation's origin's story especially since there are so many origin stories and they therefore cannot all be true. Truth matters. Yes truth is something that even science is always open to reconsider but then that's the very thing that makes science a better way of knowing than anything else that humans have so far created or discovered. Science is open to improvement or revision, whereas most religions are generally not and much more dogmatic in their essence. Yeah we can cherry-pick examples from science that shows how steadfast scientists can be when they hold onto a pet theory too long but the 'truth' will eventually win in the end. An epistemilogical argument can be had but I think you probably get my argument. See the Moral Argument for further details on how this science of morality can be developed.