The biggest question people have that do not follow Christ is how could God allow evil if him and us can agree on the fact that humans possess greatly evil tendencies. Everyone with a moral compass can agree serial killers, rapist, child molesters deserve a special place in hell. We Agree that if Satan is the downfall of God’s wonderful creation, that it would be better that he not continue to exist. The reality that if God was able to allow his only begotten to be cast to hell for our trespasses, why wouldn’t he also put down Satan like a rabid dog that he is. It is a honest question that scoffers ask and deserves a well thought out answer.
How can God be willing to cast his creation into hell? For perfect love and perfect creation you would need to put a part of ones own self into that creation to sustain itself. For love to manifest itself it would need the ability to hate you and despise you for creating it. This is how God was able to perfect humanity. He created angels such as Satan with all foreknowledge of who he is who they are and their abilities with the free will to exorcise them to a certain extent. They chose rebellion. With humans he did so the similarly with hopes that with out knowledge of potential that we would choose to love him. Instead of simplicity we chose limited knowledge in rebellion.
A better way to think of humanity compared to God is the difference between machines and us. We can create a machine and if it chooses to not operate as intended it would neither ask why we are angry with it nor complain when taken apart. Now if you were to create self replicating machines with a special ai, that was eternal and saved you could love that machine. It would be viable and self cognitive. Now imagine if you loved that machine and all of its offspring yet they all had an error in its code to self destruct in its own actions. You could fix that code but again you could only love that machine if it maintained its free will. Not only does that update come with fixing its code but unlocked potential. Now would you offer this upgrade to the ones willing to function properly or allow all to service and destroy the rest with upgraded capabilities? Would you not feel like the creator would not have full right to hate his own creation in this scenario? Would it be prudent to upgrade the less evil machines to have the greater ability to rebel and destroy if it failed to choose right from wrong in this state of being? I’ll leave this to the reader to answer.
As for Satan I believe that he is the catalyst for expediting your choice. As much as God is not willing for any to parish, it would be unfair to make his creation that loves him, and him so in return to wait forever. Nor would it be just and fair to make those who did evil towards God and fellow creatures wait for judgement.