In Reality ...
The movie had this all backwards, mostly because the film was based on Treves' accounts -- not Merrick's -- and the doctor's biased point of view naturally made its way into the script, including the inaccurate recollection of the poor guy's name. According to Merrick himself, it was Treves who was exploiting him, not the freak shows. Treves didn't care about Merrick, and they weren't friends -- as evidenced by the fact that Treves couldn't even get the guy's name right (it was Joseph Merrick, not John).
And rather than being a near-illiterate captive of barbaric slavers, Merrick was in fact clever, well-traveled, and led a surprisingly normal life despite his appearance. It was only after he injured his hip in a bad fall and became unable to work that he chose to join the freak shows, and they apparently treated him very well.
19th-century Britain was not what one would call "accepting."
He found his way into the custodianship of Dr. Treves only after being forced out of the freak show due to rising public outrage, which left him broke and in desperate need of medical care for complications arising from ... well, from being an elephant man. You know Merrick's famous line "I am not an animal, I am a man"? That was directed at Treves, whose insistence on parading Merrick's naked body around for medical experts to gawk at made him feel more objectified than he'd ever been in the freak show.