What is the difference between good sharks and sea animals and bad sharks and sea animals?

Question

what is the differance

Answer 1

Dinner.

Answer 2

The bad sharks wear black hats and have thin little mustaches that they twirl while laughing deviously after having tied Pretty Penelope Porpoise to the train tracks.

In nature, there is no "good" or "bad."  Creatures act according to the way they have evolved (or were created, depending on your religious beliefs).  If by "bad sharks" you mean the kinds that are known to attack humans, there are still no "bad" sharks.  Shark attacks happen because humans are somewhere they aren't meant to be, doing something they shouldn't be doing (naturally).  

If you were meant to swim in the ocean (naturally), you'd have been born with fins or flippers and much more efficient lungs, like a seal, porpoise or whale.  As it is, you're in their territory, acting like food.