You've actually seen Amycus Carrow before. Ze was the one killed in front of the white steps on this page.
Granger saying “I intend to let them publish it” implies that Granger has the power to stop the Daily Prophet from publishing a story. This is, in fact, true. A high-ranking Ministry official such as Granger can effectively block any story the Prophet wants to print. If Granger's other implication is correct, and Harry is willing to pursue and kill a person based on accusations in the Prophet, then what do you think of the ethics of this? Is it acceptable for you to publish a story, if you know a person is likely to kill based on what it says? Is it acceptable for another person to stop you from publishing it?