My problem with calling a pirate a thief is that it says nothing about the pirate. It describes your own feelings. It's an emotional exclamation, not a description. Nothing is gained.
It's similar to the example given in S. I. Hayakawa's book "Language In Thought and Action" where a man see's a woman and exclaims that she's the most beautiful girl in the world. Hayakawa explains that he's said nothing at all about the woman. His statement only describes his own feelings.
I suggest if you'd like to say something about a pirate, you should. Stop talking about yourself so much.
Barry