Theology question: why hasn't God stopped Satan and his demons? I'm just trying to find some theological or philosophical discussion of why God hasn't stopped Satan and his demons. Why not imprison them? Why not take away their free will? Why not annihilate them? Why allow them what dominion they have over us?

I recognize that, according to traditional Christianity, God will subject them to eternal punishment at some point in the future. But this seems on the face of it to be a far less desirable alternative: i.e., the courses of action I mention above seem better for everyone. I've looked in a few thinkers (Aquinas, Leibniz, ...), but I can't find anyone addressing this question.

Thanks!
It makes more sense when you look at it from an eternal perspective.  Yes, Satan and his followers cause us a lot of trouble in this life, but our life on Earth is not about our life on Earth.  It's essentially a test, to see if we will be faithful and obedient to God's commandments.  But that would be a meaningless question without opposition to provide a (seemingly) good reason to not want to.

That's Satan's role in the plan.  (See the first 2 chapters of Job, for example.  See also 1 Corinthians 10:13, which explicitly reiterates the point demonstrated in Job, that God does not allow Satan to do certain things that we would not be able to bear.)  He rebelled against God and sought to destroy God's work, but God is still able to find a useful purpose for Satan to serve.  But we are assured that after the end of this world, when the time of testing and mortality is over, that Satan will be cast into hell for all eternity. (Revelation 20:10)