This, of course, is a fatal argument ignored by religious folk everywhere: which religious movement is the correct one and how can you know? On the up side, if a lack of evidence from reality is merely a convenience rather than a hindrance for maintaining this faith-based belief over that one, then the downside is that any and all beliefs in agencies of oogity boogity are equivalently empty.
Contrary claims between competing faiths are very amusing to behold as supporters bandy irrational arguments about undefinable agencies and their unknowable intentions. Perhaps this picture will help reveal why:
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Questionable Motives 