Quote from : The Brilliant Book Of Doctor Who 2012 Book

But more than that, if you ally yourself with people who are prepared to fight to make a difference, then your life will always be in danger. I don't think it's fair to ever blame the person who makes the stand. Because the Doctor's so old, because he's done this so many times before, he sometimes forgets how dangerous it is. But if he didn't create the danger by opposing evil, if he didn't get these people to help him, then terrible things would happen. Standing up for what's right is always the best thing to do.