An atheist attempts to debunk Cartesian demons:
Cartesian demons are necessarily vastly more complex than explanations lacking them…
Seems to me the Cartesian demon is parsimonious. In principle, a single agent can account for every perception of every human being. Surely that's simpler than Carrier's alternative–where you need a separate stimulus (and attendant machinery) for each perception.
Here's a better response: If the Cartesian demon exists, I might as well act as if it doesn't exist, for however I act, there's nothing I can do about it. And if the Cartesian demon does not exist, there's nothing that I need to do about it.
At a practical level, it makes no difference one way or the other. If it's true, I have nothing to lose by acting as if it's false–and if it's false, I have nothing to lose by acting as if it's false.
Likewise, if it's true, I have nothing to gain by acting as if it's true–for nothing I think or do has any effect on the illusion. There's no advantage in taking it seriously. And there's no disadvantage in discounting it.