Why did Iluvatar/Eru give Men mortality?

[Ainaserkewen]

Me thinks that no-one would want to die, especially if their life is pretty good/they have goals/tasks to finish. But (especially Tolkien fans in this thread) many people would rather die and go on to the next life/world, rather than wait around in this mediocre existance for eternity. Maybe that's just christians actually, I should ask my non-christan friends, I wonder what they'd say. The fact that men have the right to chose, and the right to die and leave, would make us more special then anything immortal. The right to chose, I think, is more pressious than any gem or long span of life.

In a way, the elves are restricted, trapped in a zoo cage, while men are the visitors of the zoo. We can come, enjoy, live, then leave after an appropriate time has passed. If there were no men, only immortal elves, it would make for a very dull story, don't you think?