I could imagine dolphins like orcas being dangerous, but not bottlenose or common dolphins, I would love to be in the water with them. Orcas kind of scare me though.
Its also hard for people to anthropomorphisize sharks. They aren't mammals, they don't communicate and they known to be dangerous, eating machines. To be honest, I would rather be in the water with a dolphin than a bull shark, no matter how much I love sharks. I could understand why people wouldn't care if they all were killed off, until there was an ecological disaster. Maybe Disney movies like "A Shark's Tale" could be good for something?