Watching "Balance of Terror" closely, you will notice that Stiles did have some admirable qualities though. When he mentions "Ask Spock" about decoding the Romulan message, Kirk clearly knows that the statement is an inference about Spock's loyalty that Stiles is making yet he offers Stiles a chance to back away from his disrespectful comment.
Instead Stiles makes no effort to back away from his statement. It is clear he believes what he says and is not afraid to push his beliefs even if it hurts his career.