Most religions that exist today are of ancient origin, and their scriptures and creeds reflect the immoral beliefs of their times. However, social progress in the civilized world has led to widespread recognition of the immorality of those practices, and many churches today are in the awkward position of disavowing such evils while simultaneously maintaining the sacredness and inerrancy of the texts that teach them. The Bible, for example, explicitly states that women must remain silent in the presence of men and are not allowed to teach them (1 Timothy 2:11-12), but most modern Christian denominations ignore this rule and allow women to speak in church and even be pastors and ministers. Yet these very same Christians still believe the book that contains this hateful and misogynistic rule to be inspired by God.
Other religious groups have similarly progressed beyond the immoral beliefs of their founding generations. The Roman Catholic church, which once threatened the elderly Galileo with torture, now admits their error and accepts the heliocentricity of the solar system. The Southern Baptist Convention, which was formed for the express purpose of defending the existence of slavery, now repudiates slavery. The Mormon church once endorsed polygamous marriage but now no longer does. In these cases and others, the moral progress of modern times has forced religions to give up practices that they once defended as just and necessary institutions ordained by God.
The question that inevitably arises in such circumstances is, if a church didn’t have it right at the beginning, why should anyone put any more confidence in them now? Given that they have made errors and admitted those errors, why should I assume that they now have access to a more reliable source of revelation, rather than judging their current dogmas to be the erroneous ideas of men just as their past dogmas were?
A believer might ask the parallel question of an atheist: knowing that science has been wrong in the past, why should we trust it now when it makes findings contrary to religion? The answer is that science, unlike religion, is an inherently self-correcting system. The constant competition between groups of scientists with differing viewpoints, as well as science’s demand that all results be testable and repeatable, ensures that mistakes will be detected in due time, and even initially controversial ideas can become part of the scientific canon if their advocates can produce the evidence to support them. Likewise, even long-believed ideas can eventually be overturned by new evidence showing them to be false or incomplete.
By contrast, religion has nothing like this. There is no mechanism in religion to add new ideas or to disprove old ones; in religion, once an idea becomes part of a church’s accepted creed, it is supposed to be holy writ no longer subject to questioning or doubt. Those who do persist in questioning are labeled heretics, and often, punished or expelled to silence them. Although creeds do change, it almost invariably happens through force or schism, or more rarely through a church head promulgating it by fiat as new dogma – almost never through a theologian convincing the majority of his peers that their core beliefs are mistaken by marshaling evidence and rational argumentation. Dissension within the framework of the existing creed is usually allowed, but a challenge to the creed itself never is. If anything, the believers who are rewarded and praised are the ones who most fiercely defend traditional beliefs.
The answer is that religion, unlike science, is fundamentally not based on evidence. There is no way to decide on the truth of a religious proposition independent of personal opinion, and so attempting to introduce a self-correcting mechanism into religion would lead only to chaos, a Babel of irreconcilable diverging opinions (as indeed the human race as a whole is, when it comes to this subject). By contrast, centuries of scientific debate have produced continual advances in knowledge and a rock-solid consensus on many issues of fundamental importance. Just try to imagine if the human race as a whole was this united on religion! It never has been and it never will be, so long as religion persists. But the fundamental non-evidentiary basis – in other words, the fundamental irrationality – of religious belief serves as a strong reason to forsake it entirely, and instead trust in methods that have proven effective at delivering truth about the external world.