I grew up assuming that hell was a never-ending torture chamber where immortal souls scream and writhe in constant agony and torment. William Crockett (who holds a metaphorical view of hell's horrors) cites Nels Ferre who insists that if the traditional view of hell were true, it would make Hitler "a third degree saint, and the concentration camps...picnic grounds." (See the book, Four Views On Hell).
Conditionalist Clark Pinnock says that the traditional view of hell portrays God as "a bloodthirsty monster who maintains an everlasting Auschwitz for his enemies whom he does not even allow to die." Pinnock's reply to the charge that sentimentality drives the conditionalist, asks if perhaps hard-heartedness might be driving the immortalist position. He says that "Everlasting conscious punishment is a huge stick that some people do not want to give up." (Also in Four Views on Hell).
Everlasting torment has definitely been a weapon of control in efforts to modify human behavior. Some ask how a hell that is not forever could possibly deter sinful behavior. Unless people think hell is forever, what reason do they have for being good? This argument is based upon presumed human responses as opposed to the revelation of Scripture. It does not settle the matter of hell's duration in the least. It is an argument from human reasoning, just as a conditionalist argument based solely upon sentimentality would be from human reasoning. Only the biblical data matters.
Moreover, it is far from being a given that belief in never-ending torment deters sin in any way. I've known plenty of folks who believe in a never-ending hell, but continue to live unrepentant lives. There are also conditionalists who live repentant lives. Behavior modification has less to do with one's view of hell and more to do with one's view of God.
I believe that love for Christ will go much farther in deterring sin than whatever view one holds regarding hell's duration. As F. LaGard Smith suggests in his book, AfterLife, perhaps the primary purpose for hell's existence is not to serve as a deterrent, but as an assurance of ultimate justice.