Why lord of the flies is not a Utopia
The kids did at least think the island was a utopia. This turned to chaos because of human nature. Too many of the boys simply wanted to have fun in irresponsible ways. This led to discord between them and the ones who wanted to be "civilized" and responsible. That, in turn, led to the chaos that came as Jack's group started fighting Ralph's, eventually taking control of the island. Golding argues that irresponsible, selfish, violent behavior is in our natures. This aspect of our nature was given free rein on the island and chaos ensued.
What a Utopia actually is
A perfect society can be defined as a society where every person lives freely and their possibilities are best realized to the full. It is normal in human society for the rich to be free and to realize their potential while the few have limited freedom and time. A Utopia is a perfect society