"Tested" is the key word, here. Anyone can believe anything they like. But can you test your hypotheses?
Here, too, it was a subject which
could be tested. Even if the technology for accurate testing wasn't yet available, a test of the problem could be conceived, and executed. To my knowledge, there are no valid tests for the presence, or absence, of gods. Any tests which have tried to demonstrate the existence of supernatural forces have all failed. You can pick whichever side you want, but when test after test shows that these forces do not exist, and no tests show that they do, then sooner or later you have to admit that you might be wrong.
Read this to see one way that relativity was confirmed.
While we cannot prove that gods do not exist, it can be shown that the gods
as defined by religions cannot exist. One of the reasons for the demise of the ancient gods, Zeus, Odin, Jupiter, etc., is that science showed that the effects which people had ascribed to them (thunder, lightning, wind, storms) were natural effects, following natural laws. Any objective reading of the Bible will show that God,
as defined in the Bible, cannot exist. There are just too many internal contradictions, as well as discrepancies with observed nature. So, while it can be reasonable to say that there are no gods because we can find no evidence for them, it is not as reasonable to say that, despite a lack of evidence, there must be gods.