Most importantly I find the following line from the letter disturbing: "To those who seek to block attempts to secure a pardon with the argument that this would set a precedent, we would answer that Turing's achievements are sui generis." They are arguing that Turing uniquely deserves a pardon because of his genius. That itself would set a terrible precedent because it would appear that the eminent Lords believe that being a great man puts you above the law.