The point is, after the serial killer is gone, the deception of a death miller is doomed to fail. There really is no point in having a death miller. Deaths would have stopped, outside of the ones you yourself caused. And look at how easy it was to find out about a cult. Would the death miller being lynched really have stopped this revelation? I don't think it would have had any effect.

And Serial killers dying early happens almost every game they are in. I don't see how they couldn't have forseen that happening. Honestly, the Death Miller is a useless role for this game, so I see no reason to believe the claim.