A photograph made public Sunday showed Michael Phelps, who won eight gold medals in swimming events in the summer Olympics in Beijing, smoking marijuana. Mr. Phelps, 23, said he regretted the behavior, which occurred at a party in November. Are athletes such as Mr. Phelps obligated to behave like role models? Or is that asking too much? Should he have the freedom to indulge in some youthful indiscretions? Does accepting endorsement money come with responsibilities? Should the companies paying Mr. Phelps end their contracts with him?