It is important to remember that More did not agree with everything in Utopia. There is no doubt that More was opposed euthanasia, yet it was practiced by the Utopians.
Utopia is an imaginary society where people have designed the best society they could conceive of with the use of natural reason. However, they have been denied the truths of divine law. As Peter Ackroyd points out in his recent biography of More (The Life of Thomas More, Nan A. Talese, Doubleday, 1998.), "That is why they encourage euthanasia, condone divorce and harbour a multiplicity of religious beliefs- all of which actions were considered dreadful by More himself and by Catholic Europe. This may be no ideal commonwealth, after all, but a model of natural law and natural reason taken to their unnatural extreme."