[Inziladun]

I don't really see that as meaning that Men had free will, and Elves did not. The individual retained free will always according to the will of the One. As a race, though, the Elves were pretty much restricted to a certain course.

The Elves alone of the Children were immortal, and did not naturally die in Arda. Therefore, they really weren't suited for life in a mortal environment. I see their place as ultimately teachers of the other races (though they certainly had their share of heroic parts in shaping the history of the world), which is why they eventually had to relinquish their attachments to the mortal lands and return West, or else wither away to insignificance.

Men, on the other hand, were in a suitable place living in a world in which things "died" as they did. More importantly, the fate of the race of Men was left open-ended: no such ultimatum was given to them as was the Elves. To Men ultimately was given the power to make the world their own, and see things through to the End, taking part in things that had not been revealed to the Valar in the Music, but were the province of Eru alone.