These elephants have been violently abducted from their families and often brutally trained for this purpose. To persuade an elephant to work - including to carry tourists - a mahout must ensure that it follows instructions at all times. This, by necessity, means breaking down an elephant's independent will. To do so, calves are chained, beaten, deprived of social interaction.
Other animal groups, like the Elephant Nature Park in Chiang Mai, Thailand, also oppose elephant-riding on similar grounds, calling training for the activity "torturous." But the park also offers an example of "eco-tourism" that doesn't take elephants out of their habitat or bring them to a luxury hotel. Visitors can take trips to the Elephant Nature Park and see the animals, engaging in activities like feeding the elephants fresh fruit, helping to bathe them in a river, going on walks or simply watching them play together.
And, if a tourist were so inclined, he or she could also take a selfie with one of the elephants.