Is utopia desirable, or do humans need conflict and challenge in order to find purpose and fulfillment in their lives? Where do you see evidence of this in Candide?

Although Candide goes through many terrible experiences that show that all is not to be for the best in the best of all possible worlds, one can nevertheless see evidence of the need for conflict and challenge in order to find purpose and fulfillment in life. The chief evidence of this is Candide himself. He cannot find happiness cultivating his garden and living the quiet life until he has gone through many horrors engaging with the wide world of adventure. He has to satisfy himself that seeking adventure is not the best path in life.
On a more specific note, if Candide had not had his adventure in Lisbon where he is flogged by the Inquisition, he would not have found out that Cunegonde had survived being raped and disemboweled. Because Candide happens to be in Lisbon at the time of an earthquake, he is able to escape his inquisitors and rescue Cunegonde from her sex slavery. Although she and Candide have many more horrible adventures, in the end the two are able to marry and pursue a quiet life. Clearly, Candide is happy to have Cunegonde as a companion in his garden.