His eyes pierced onto your form, high annoyance written across his face. “Well?” Donatello snapped impatiently, gesturing to the bloody body of someone you knew. Someone he killed. “Are you going to help me clean this mess or not, Dove?” 

He has given you the same excuse when asked why. Why anonymously threaten your friends, why kidnap you, why murder this person. To protect you.

And to the mutant turtle, it's true. He doesn't care if you think otherwise.