Welcome back to "Doggerel," where I ramble on about words and phrases that are misused, abused, or just plain meaningless.
Many of you will instantly recognize this as argumentum ad antiquitatem, or the appeal to tradition. This one is somewhat of an appeal to authority as well, presuming that if human civilization believed something for a long time, there must be some validity to it. Of course, the big problem with this is that humans have believed all sorts of silly things over the ages.
Humans are fallible creatures, and they have several kinds of known problems in their thinking process. Just because lots of humans once believed in something doesn't mean they did the sort of error checking that science requires. Bogus medicine gets passed on through generations because of the placebo effect fools lots of people. That's why we have the double-blind control study, for instance: It's designed with our capacity for self-delusion in mind. The vast majority of silly things mankind typically aren't subjected to error-checking processes. Some people were hideously tortured and burned alive for even suggesting the possibility of error in some of these beliefs.
For traditional and alternative "medicine," it's often no different: The practitioners are almost never willing to put their treatment to the test: They're content to draw results from unblinded, uncontrolled testimonials, a method known for producing false positives, thanks to the human failings of confirmation bias, the regressive fallacy, misattribution of natural improvement, and dozens of others.
In matters of religion, the ancients' "knowledge" is usually built on ignorance combined with unrestrained imagination. Just because the ancients didn't know what caused lightning doesn't mean it was Zeus. Just because we allegedly don't know how IC evolves doesn't mean there's Intelligent Design at work. Just because your particular religion has been around for thousands of years doesn't mean it's been error-checked.
Put simply, a belief's age has nothing to do with its validity. If the belief is wrong, it's only a testament to human stubbornness.