If you really want a tame shark diving experience, Shark Ray Alley in Belize is pretty fun. It is primarily nurse sharks that act more like puppies. You can roll them on their backs, rub their bellies, pet them, etc. I'm not overly enthusiastic about situations where people feed sharks, but this is probably the exception. Nurse sharks are fairly harmless and judging by the hundreds that swarm the boat when you pull up, it doesn't seem to have resulted in any harm to the local population within the marine park.
I honestly think this is the worst part. You're changing how the sharks act in their natural state. You feed them, you touch them, you do things to them that are outside of their normal life.
That kind of diving is pure and simple harassment to the wildlife. Sure it's great for the people who get to do it, but in terms of the widlife ecosystem, it's damaging. Think about feeding ducks / turtles bread at the lake. Sure yeah, they'll eat it, you think you're helping them, but you're just filling their stomachs full of the least nutritious food possible.
(13) The term "take" means to harass, hunt, capture, or kill, or attempt to harass, hunt, capture, or kill any marine mammal.
....
A) The term "harassment" means any act of pursuit, torment, or annoyance which
(i) has the potential to injure a marine mammal or marine mammal stock in the wild; or
(ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering.