This argument really isn't very good. It works on precisely none of the religious people I know, because: A: They don't believe that God would tell them to do anything wrong. B: They believe in Satan, who they are quite certain would tell them to do something wrong. C: They also believe that Satan can lie to them and convincingly pretend to be God. Accordingly, any voice claiming to be God and also telling them to do something they feel is evil must be Satan trying to trick them, and is disregarded. They actually think like that, and can quote relevant scripture to back their position, often from memory. This is probably better than a belief framework that would let them go out and start killing people if the right impulse struck them, but it's also not a worldview that can be moved by this sort of argument.

I think that this quote might benefit by tabooing the word "god". Does it mean "an omniscient, omnipotent being"? Does it mean "an omniscient, omnibenevolent being that would never ask you to do anything truly evil, but may on occasion ask you to do things that you don't see the sense in, and that in fact appear evil at first glance"? Does it mean "a being worthy of respect and obedience, even in the most dire circumstances"?