Zac Efron -- Dogfight Over Shark Encounter (VIDEO)

Zac Efron was either a noble conservationist or a reckless yahoo when he dove with a tiger shark.

Shark experts could not be more divided. Naturalist Juan Oliphant, who set up the dive in Hawaii with Zac and Adam Divine, tells TMZ the point was to show the beauty of sharks so people will think twice before poaching them for fin soup.

But shark photog Jeff Kurr felt Zac's dive was not only reckless, it could actually make sharks even more hated and feared. He says tiger sharks are extremely dangerous and unpredictable.

Oliphant says Zac and Adam were extremely respectful and the shark was "mellow and uninterested in people," but Kurr says grabbing a fin is an aggressive invite to a deadly attack.

FYI ... in Hawaii, tiger shark attacks outnumber great white attacks.