I think people prefer a dogmatic morality to a real system of morality because it's easier. However, it is a most immoral of systems, it is derived from the morality necessary for the most basic and primitive tribal system to function, it is designed to favour those in power and oppress those without political influence and, by doing so, maintain order in the tribe. It blames rape on victims, it condones the beating of slaves and condemns slaves who seek their liberty, it allows for executions based on hearsay, it essentially codifies tyranny.
As the world has developed, this moral code has been seen by all to be inadequate, even the faithful have attempted to explain away their own moral codes, attempting to draw abstract truths then drawing conclusions from those abstract truths that are directly opposed to the original moral code they claim to live by. But, in truth, while it would be preferable to dispense with these archaic codes entirely, I am glad for the dishonesty and self-deception of those who follow them, it would be far worse for us if these codes were taken literally as they are in the Islamic world.
Unfortunately, while the bloody details of these moral codes are no longer in effect, there is a lingering danger from them, namely their simplicity. 'Morality' is nothing more than a neurological inhibition that aids in the continuance and protection of our species, in fact it can be seen to varying degrees in every social animal. Without at least a very rudimentary 'morality' no group of animals, be they humans, apes, or horses could live in a social context, which, for many of these species, would mean their extinction. So with these humble beginnings, it's no surprise that people prefer an easy and simple system of morality; however, our society is no longer so simple and basic, we have created great civilizations and nation-states, we have instituted international bodies and laws amongst nations, the morality of the tribe does not always apply to our current situation. In the ancient codes we see severe punishments for intra-societal violence, but inter-societal violence is accepted even to the extreme in the Old Testament where not only tribal acts of violence against other tribes was tolerated, but even individual acts of violence against outsiders in certain situations. If one starts with the assumption that you are always in direct conflict over scarce resources with other tribes, essentially in a constant state of war, then this is a reasonable moral code when members of another tribe are, at all times, essentially enemy soldiers. But as more defined civilizations emerged, the simplicity was lost. Occasional states of peace, rather than constant war, between equals became more viable. And things further changed with the development of economies so that even between unequal powers, peace may be more advantageous between both powers because of economic concerns. With the economic and industrial changes of the 18th and 19th centuries these changing conditions started to affect even things such as property. Slavery, while still advantageous in an agricultural economy was less useful in an industrial economy, making it's continuation a hindrance rather than aid in truly advancing a civilization due to excessive competition against a fledgling, but increasing vital, sector of the economy. In certain circumstances even personal use of material property had to be questioned (aggressive monopolies, paying employees in vouchers for a company store, etc.) as it was no longer the case that while using my property as I see fit may not help you, but it doesn't harm you. Rather it did harm people and not just no an individual level, but monopolizing the workforce and forcing competitors out of business caused harm to entire segments of the economy, it caused harm to society itself and thus the moral codes and regulations had to again be updated. In a constantly changing world, we must have, by necessity, a constantly changing morality.
But throughout history there has been one absolute standard of morality: the advancement of one's tribe, city, civilization, empire, nation-state, etc....the advancement of society. Even relativistic morality shares in this absolute, but it's not so much an absolute principle of morality as it is the evolutionary definition of morality. If something is not aimed at advancing and continuing society, it's simply not morality. It may or may not be 'good' (whatever that means), but it's not 'moral'.
Now we may argue what constitutes 'society' is it merely our own family? Our tribe? Our Nation? All humanity? All intelligent entities? My guess is that with our current social development we're somewhere between Our Nation and All Humanity; though I believe our society being defined in terms of intelligence is approaching faster than most dare dream...as it should.
But this debate is not the essence of moral relativism, one can take any one of these definitions of society and form an absolute moral code, I wish they wouldn't, but they can and do. Moral relativism is simply the acknowledgment that the morality of a situation depends on, is relative to, a multitude of factors. One must determine how they interplay and what the ultimate impact on society is. Furthermore, the direction one believes society should advance must also be taken into account. An environmentally-driven morality and a technology-driven morality are both valid, though sometimes opposed to each other; but as both seek to advance society in their own way they can both be considered 'moral'. As to which one we should embrace, that's not so much a question of morality, but a question of how a society believes they should develop; it's more a political question than a moral one.
Of course, we can't have a conversation like this without abortion coming up, it's a favourite topic of those who take a simplistic approach to morality. But it's never been a simple question; granted, in the ancient world abortion was less common because of the lack of medical advancement, but an equivalent practice, exposure, was VERY widespread. Those who take a simplistic approach to morality would say, 'you're killing a baby, that's wrong.' But when resources are scarce, the answer isn't so simple. In a small tribal system, you had to have a balance of those who can work and those who can't. Too many children, too many non-productive mouths to feed, could lead to widespread shortages and starvation, threatening the entire society. Insufficient children, this imbalance in the workforce is simply delayed and you'd have the same problem a decade later. The stakes (survival of an entire civilization) may not be quite as high today, but the complexities still exist and will exist as long as we have a scarcity of resources. Do we spend money allowing fetus with inadequate brain development to be born, then spend resources to raise it, possibly even having to expend resources throughout its entire life without any productivity in return? Or do we use those resources to send a promising but disadvantaged youth through college? Or should I say several disadvantaged youths through college? Allowing them to climb out of poverty, make a better life for themselves and their family, and even contribute back to society allowing the cycle to continue? Is it beneficial to harm the career of a promising doctor or scientist who became pregnant on the roll of the dice that her offspring will be more beneficial to society? You're rolling against the house on that one. This is not a false dichotomy, every time resources are put to one use, they are deprived from another and it's not enough to look at the specific situation, you must take into account all related impacts of your decision...that's why morality is relative and why a dogmatic approach will do far more harm than good, a decision made in ignorance is rarely the best decision.
With that said, contraception is an obviously better 'more moral' choice since it takes far fewer resources for the same impact.