The question is not whether it's possible, but desireable. If it's desireable, in all likelyhood it's possible. If it's not desirable, it should be made impossible.
As you say, such changes that will accompany a transition to a utopia will significantly, if not completely, alter mankind. Which essentially means that, yes, you can make a better world, but you will never live to see it, because you will die in the process and something else will be born. Or, if you somehow survive, this utopia will bring you no happiness. Am I the only one who thinks its ever so slightly insane for a species to wish for it's own demise, to actively work toward it? Man is, if you choose to be honest about it, as much a creature of fire and blood as a creature of enlightenment, creativity, tolerance and grace. We're equal parts Genghis Khan and Mozart (or whatever, you get the gist). If you deny one, you deny the whole. If you work to eliminate one, you work to eliminate the whole. I can't know what's best for the future, and I don't care. And yet, to bring about this utopia would be to sacrifice the present on the altar of the future, and to sacrifice the desires of man-at-present to the desires of man-of-tommorow. What is good is entirely subjective. It seems natural to me that any person (or age) will favour what is good for them over what is good for a stranger (age), and an unborn one at that
/rant