Continuing the theme of the various ideas people have as to why hell might not be eternal for some, there is a school of thought that says that good deeds can offset sins such that one might get to heaven despite being a sinner. So reciting the Lord's Prayer or giving alms, for example, might get you out of hell by offsetting your other sins.
And yet, we see that the church has never accepted the idea of hell as mere purgation when it comes to the devil. This is not because we are hateful or anything like that--we want all who can be saved to be saved. It is because we wish to be faithful to Scripture, where God has clearly and repeatedly said that hell will be eternal, everlasting, for ever and ever, etc.
"Thus is is Scripture, infallible Scripture, which declares that God has not spared them."
Where Scripture speaks we must bow our emotions and thoughts to the Wisdom of its Author. And if it's true that the devil will never be purged of sin by the fires of hell, how much more true must it be of lesser beings such as men? We do not want to be charged with believing that "men's imaginings have more weight than God's words!" Rather than trying to make ourselves feel better about something we don't like, we ought to "bow in obedience, while yet there is time, to the command of God."
Besides, we have a vested interest as believers in "everlasting" actually meaning "everlasting"--would we want it to be qualified we we speak of "everlasting" joy or "everlasting" life? "Therefore, since the eternal life of the saints is to be endless, there can be no doubt that eternal punishment for those who are to endure it will have no end."