S you made a comment about doubts that cause people to keep from speeding and good doubts versus bad doubts. I think of it this way: a good doubt, like the one you mentioned that reminds you you shouldn't speed in your car, is your conscience. A bad doubt is one against your faith, like thinking that God doesn't exist, and is sin.
You also mentioned Satan masquerading as an angel of light- I suppose he could plant good doubts if he wanted to, but why do that? It would be counterproductive to his cause against God.