Eternal Damnation

There are those who believe that when God punishes man posthumously for sins during his lifetime, the person will suffer eternally. This idea makes no sense. First of all, why should there be eternal punishment for a sin that was temporary? Why would God create a world to punish His creations, rather than to do good to them? So many people sin, did He create the world to wreak his vengeance on them? Doesn't it say "The world was built on Chesed (kindness)?" At the time of creation God said "It was very good." With a world in which so many succumb to sin, if they are all condemned to eternal damnation, doesn't sound like a very good world built on kindness! Furthemore God created the evil inclination and the temptations that are placed before man in this world, is He so cruel as to then use His invention as a means of punishing others forever?