I say Hell is eternal because.... it's the official position of the Roman Catholic Church, the Church Jesus founded at Pentecost. Wee, don't have to think for myself. Thank you, thank you <bows out>
Seriously though, A Case for Faith has a chapter dealing with this question in favor of Eternal punishment.
http://www.scribd.com/doc/3925352/St...Case-for-Faith
Go to page 113, it's in the 6th interview.
Here's the objections answered (to pique your interest into actually reading it)
Objection 1: How Can God Send Children to Hell?
Objection 2: Why Does Everyone Suffer the Same in Hell?
Objection 3: Why Are People Punished Infinitely for Finite Crimes?
Objection 4: Couldn't God Force Everyone to Go to Heaven?
Objection 5: Why Doesn't God Just Snuff People Out?
Objection 6: How Can Hell Exist Alongside of Heaven?
Objection 7: Why Didn't God Create Only Those He Knew Would Follow Him?
Objection 8: Why Doesn't God Give People a Second Chance?
Objection 9: Isn't Reincarnation More Rational Than Hell?