Utopia's Biggest Flaw
In the Community, memories were given to The Giver to bear. Feelings were dismissed as nothing more than a dream. People in the Community were not able to think for themselves or make their own choices. Jonas realized this when he learned about memories from the Giver. As the Giver said, "They can't help it. They know nothing...It's the way they live. It's the life that was created for them."
I think this is why Jonas chose to leave the Community. He realized that this lack of freedom was not a sacrifice that he could live without. In fact, without this freedom of will, we would not have diversity in our world today. Everyone would be the 'same.' Anyone who is different would be locked up or punished. We would not be individuals who can think, act, speak and live in our own way. Therefore, I think the lack of freedom is the biggest drawback to utopia.