Robert,
I don’t think that anyone will disagree that God is ultimately in control and must at least tolerate/permit everything that occurs, including the actions of demons and sinning humans. And you’re right that God, being omnipotent, doesn’t actually have to put forth time and effort “fighting” Satan, and therefore His delay in bringing the world to its consummation must be for a good purpose even though it means permitting evils that would not otherwise occur.
Where you are getting pushback, I think, is when it comes to any notion that my sins, for example, are therefore good or approved by God. He might use even my sins for good, by reminding me how dependent I am on His grace to resist temptation or molding me eventually into a spectacularly changed person like St. Paul, but that does not mean He wants me to commit the sins themselves. Likewise, He may use the fallen angels’ rebellious actions to promote rather than inhibit sanctity in their human victims, but that does not mean He created those angels to fall and become His unwilling agents in that way. I firmly believe that God would very much have preferred a world in which both Lucifer/Samael/whatever you want to call the unfallen Satan and Adam simply lived in His presence forever in mutual love. Of course, that’s kind of a weird counterfactual, since God presumably knew how the whole thing would go from the beginning, so I don’t actually know how God “thinks” in that situation. But I think whenever He has said “Don’t do the things” (to borrow from a recent Facebook meme), He really meant that creatures ought not to do those things and would be better off if they did not.
Usagi