A religion which strongly reflects the beliefs of its time is more likely to be a product of its time than of revelation.
If a given religion was purely the invention of human beings, we would
expect that that religion would bear similarities to its culture of
origin. On the other hand, a transcendent or all-knowing deity, or even
one that was merely far wiser than human beings, would not be limited by
what was known or believed at the time he dispensed a revelation, but
could provide new information of which people were not previously aware
and which did not correspond to any concepts in their experience.
However, when we examine religions, we find that the former and not the
latter situation invariably applies.
Christianity, again, is a
perfect example of this. The theology of this religion blends
apocalyptic fears, Jewish monotheistic ideals, Greek ethical philosophy,
and the worship practices and beliefs of the mystery cults at precisely
the time when those things were mixing at a cosmopolitan crossroads of
the Roman Empire. Granted, God could decide to reveal his wisdom to
humanity at a time and place when it would exactly resemble a
syncretistic fusion of the prevailing theologies of the day. However,
all else being equal, the principle of Occam's Razor should lead us to
conclude that it is nothing more than that. Positing a deity is an extra
assumption that is not necessary and gives no additional explanatory
power to any attempt to explain the origins of the Christian religion.
Another way in which this aspect of the Argument from Locality applies
is in regard to those religious tenets which state beliefs and approve
practices that were widely agreed upon at the time, but that today are
recognized to be false or morally wrong. One particularly glaring
example is the way the Christian and Jewish scriptures both implicitly
and explicitly approve of the practices of human slavery and the
institutional inequality of women. Likewise, these writings show no
special insight into the workings of the universe other than what was
widely known to the people of their time, and make many mistakes common
to those who lived in that era - for example, the belief that mental
illness and physical disability were caused by demon possession. Again,
under the Argument from Locality this is exactly what we should expect:
these religions, being the product of those time periods, cannot be
expected to show knowledge advanced beyond what the people of those
periods possessed.
In closing, consider what would refute the
Argument from Locality. We could have found ourselves living in a world
with only one religion, spread throughout the globe, with prophets from
among every people. We could have found that, when we first contacted
isolated native tribes, their religion was identical to one that already
existed rather than being entirely their own. We could have found
religions that bore no resemblance to the culture of their time and
place of origin, in possession of advanced scientific knowledge or
advanced ethical principles totally unlike what was commonly believed at
the time. These are reasonable things to expect if there really was a
god genuinely interested in revealing itself to humanity and being
worshipped.
But in reality, we find none of these things. What
we find are numerous contradictory and conflicting religions, some with
specific "chosen" races or ethnicities, and the further separated they
are in time and space, the more their beliefs clash. When we encounter
previously isolated tribes, their religions are always new and unique.
When we examine the ethical codes and scientific knowledge of religions,
they always bear strong resemblances to the times and places where
those religions originated. Under the assumption of atheism, this is
precisely what we should expect.
One could, of course, argue
that this does not prove anything, that God deliberately intended things
to be this way. Maybe he has reasons of his own, unknowable to us, for
sending his messengers to only one people. Maybe he decided not to
disclose advanced knowledge to primitive people. Maybe he allows evil
spirits to delude people into creating false religions. Maybe, maybe,
maybe - but that is precisely the point. When one believes in
supernatural beings that can violate the laws of nature at will and that
have motivations inscrutable to humans, all grounds for believing one
proposition over another vanish, all knowledge disappears. There is no
longer any reason to expect any state of affairs rather than any other.
Such a doctrine is impossible to falsify and leads to nothing but
epistemic chaos. In explaining anything, theism turns out to explain
nothing.
But atheism does not have the luxury of infinitely
imaginative explanations unconstrained by fact. Given a few first
principles - physical laws and observations whose existence no one
disputes - atheism requires that the world can only be one way, and that
is the way we in fact find it to be. Believers may argue why God set up
the world in just the one way we would expect it to be if he did not
exist, but for a freethinker, the conclusion is obvious.