This thing of darkness Why Should I Care
Why Should I Care?
Okay, okay. We get that you don't have a creature-slave trying to kill you. But there's another interpretation of this quote we'd like to entertain. Some audiences see Prospero as nothing but a bitter tyrant.
It's easy to see why. He's taken Caliban's island in return for his own lost title, he manipulates his daughter, is cruel to Ferdinand and Caliban, and kind to Ariel only when the spirit is totally subservient. He also puts his enemies through all kinds of hell to gather them up so he can judge them.
Perhaps he's talking about himself here. Sure, he's directly talking about Caliban when he says the quote, but maybe he's also saying that he's responsible for the darkness (or evil) inside his slave. If that's true, then this quote would be more about Prospero coming to grips with the fact that he's got evil inside of him (as well as good).
We all have a mix of good and evil inside of us. The trick is making sure that darkness doesn't overwhelm you, like Caliban.