It should be well established by now that we live in an increasingly secular society, and the role of the church is being gradually marginalised on a social level. Yet despite the correlation between the decline of the church and the progress of mankind, the notion that religion is still the source of morality in the community is still a majority view. Religion perpetuates its own relevance by perpetuating the idea that it's necessary. Since the natural world is lost to science, it's in the role of society where it preaches it can still play a role. That may be true, though finding other niches for religion to fill does not necessarily mean that it has a place talking from a moral foundation.
A history of inaction
What major religious institution has come to the cause of the progress of mankind in the last few hundred years? In that time I can think of many instances of the advancement of mankind, such as the abolition of slavery, the right to practice religion freely, equal rights for women and minorities, protection of freedom of speech and expression, and now the movement towards giving equal rights to persons of LGBT. Yet looking back through history, it's hard to find any major religious institution that stood up for these rights before secular society has done so.
Now while many of the people who have been part of these movements were religious themselves, just what role has the institution of religion played in progressing the rights of man? To be as charitable as possible to the institutionalised religions it would be fair to say that the progress of man happened irrespective to religious instruction. It would be more accurate to say that in a lot of these cases, progress has happened in spite of religion. The suppression by religion in the dawn of the age of enlightenment was abhorred by modern standards, yet this is still the system being largely advocated by fundamentalists. These institutions are being dragged, kicking and screaming, into the 21st century.
If anyone can give me an example of where the rights of mankind have been called on by a religious leader before there was a secular movement, please do. Because all I can find when I look back through history is that the major markers of social change happened in spite of religious preference. The avocation of slavery was most ardently argued through religious instruction, the rights of women are still being contested by religious fanatics today. The right to free speech is in constant battle with religions calling for a sedition on blasphemy, and the most strident opponents of equal rights for LGBT come from the bible thumpers.
Looking at history, it seems that religions act not in the best interest for humanity, but for their own preservation. This trait is hardly surprising, and from a memetic perspective it's understandable why such a survival strategy would come about. The irony of the situations is that many of these religions were born out of a radical overhaul of the then conservative establishment. Christianity especially has this foundation, Jesus was centuries ahead of his time in terms of advancing the moral zeitgeist of society. Yet the Catholic Church should draw particular ire for the way it supported fascism in the early 20th century, or how it systemically covered up sexual abuse of children by priests, and even the anti-condoms stance in AIDS-ridden Africa.
A basis for behaviour
The idea of free will needs to be discarded, it's inadequate to describe how humans behave, and as such the notion that beliefs can dictate behaviour absolutely is absurd. It fails to recognise the process which have shaped our behaviour, and the internal processes that govern our behaviour. To go without food is not mind over matter, the body needs an energy source in order to survive so the feeling of hunger is programmed into us. Likewise the survival of our species depends on reproduction, so automatic functions exist within our body that lead to the desire for sexual interaction. One may call it original sin, but in reality these drives are reflective of our ancestry and of our mammalian status.
To say "without God, people will behave like animals" is specious reasoning, because we are animals! By definition, everything we do is animal behaviour so we can't not behave like animals with or without God. The more that has been learnt about social behaviours in other species, the more apparent it is that almost all of our behavioural patterns are simply extensions of behaviour exhibited by other species. Any moral doctrine serves at best as a modifier on already existing behaviours, the extent to which is dependant on the individual and the society they reside in.
The prospect of genetic determinism is a frightening one, and it's largely incompatible in regard to how we view moral choices. But the science points to there being at least some genetic trappings that individuals cannot get out of, so it would be naive to ignore that the phenomenon exists and is one factor in determining behaviour. It would be a dangerous endeavour to shy away from that notion and still work towards the dogmatic absolute of behaviour. There are certain standards that society holds itself to, an implicit and explicit set of rules by which those within a society have to hold themselves accountable. Because quite simply, everyone within a society is accountable to themselves and to others. Otherwise there would be no society, just individuals.
The interdependent nature of humanity has been that way for presumably hundreds of thousands of years, we are historically a tribal species who live and operate as a group. As such there needs to be means in which individuals can operate with one another, and thus the social construct of morality is born. One of the great insights into human behaviour of the 20th century was mathematically linking behaviour to game theory. Like Darwin did 150 years ago with the case for evolution, game theory over repeated interactions shows that what we consider moral behaviour is not only possible but inevitable.
It's not to completely discount the role that higher thinking plays, but it would be quite a leap to suggest that we are smarter than the process that bore us. After all, evolution has had hundreds of millions of years shaping the minds and bodies of our species and we've had but a few thousand years of trying to make sense of it all - and for the most part that endeavour suffers the same fate as the Ptolemaic universe in that it has traditionally been based on a bad assumption. The assumption of gods behind our behaviour is another failed hypothesis that now survives beyond it's usefulness. There may have been a time when it was necessary, but we are in a post-religious reality where our understanding is shaped not by the appeal to the supernatural, but by looking at the world around us.