Have been thinking about this recently. Why does God not only slow Satan to exist but allows him to go abroad?
I'm not well informed in the subject BUT I'd say it is us, through our exercise of free will that magnify the devil. I understand him to have been defeated at the cross.
Angels are moral beings without physicality. Humans are moral beings with physicality. A moral being has free will, in order that what we offer, we offer as gift not tax. Moral beings have a choice to make. Some humans make good choices and some make poor choices. Some angels make good choices and some make poor choices. God did not make us to be zombies.
"Saint Michael the Archangel, defend us in battle. Be our protection against wickedness and snares of the devil; May God rebuke him, we humbly pray; and do thou O Prince of the heavenly hosts, by the power of God, thrust into hell Satan and all the evil spirits who wander through the world seeking the ruin of souls. Amen" Feast day Sept 29th
St. Michael is our parish patron, so we had a high Mass on the day. What saddens me is that, not even a quarter of the parish attended OR know who St. Michael is (true story)
In my view Satan was part of who we are, Satan was the worst part of ourselves, or the worst version we could have been of all possible worlds - that we defeat when we follow in the life of Christ. So in some sense God has already defeated Satan in each of our lives. The Satan is the collective consciousness of the worst aspects of humanity. That is my view. I think Jesus is speaking allegorically when he describes the fall of Satan, what he is really describing is the fall of carnal man and the seperation of man and God, Satan representing the worst aspects of humanity. I realise my interpretation is a bit left field. I could be completely mistaken. Perhaps Satan really is as the literalists say, a fallen Archangel - I have no qualm with that interpretation either, I just find it more difficult to believe since it runs into the problems you just mentioned. The important thing is we can all agree that it is through Christ's sacrifice and the gift of faith, not theology, that we are saved.