Withers specifically admonishes
the dead 3 saying did they really think the other gods wouldn't notice the loss of souls with their plan of turning people into mindflayers?

That seems to be the crux of his point.

And I guess between Selune, Shar, Mystra, Oakfather, (Vlaakith), (MC cleric's deity) and his rez'zing - presumably with Ao's tacit support/non interference, he was right.