Quote from : Harry Potter and the Half-Blood Prince Book

Harry, despite your privileged insight into Voldemort’s world (which, incidentally, is a gift any Death Eater would kill to have), you have never been seduced by the Dark Arts, never, even for a second, shown the slightest desire to become one of Voldemort’s followers!” “Of course I haven’t!” said Harry indignantly. “He killed my mum and dad!” “You are protected, in short, by your ability to love!” said Dumbledore loudly.