Why is it that a villain is always more easily crafted than a convincing nice protagonist? I find my own protagonists are generally unlikable, if interesting and potentially admirable in some ways. They're rarely nice; they border on the villainous.
Grey, the main character in my novel Behind the Ruins is an example. Admittedly I spent the entire writing of the book striving for realism in characters, action and setting, so discovering the kind of man that could survive the apocalyptic destruction of the modern technical world isn't outwardly warm and fuzzy shouldn't be a huge surprise. He's a killer, tormented by the memories he carries but still willing to kill again if he deems it necessary – or even convenient. He's loath to lead, emotionally cowardly and ruthless, but he's still more interesting to me than your average white-hat good guy. Snape always interested me more than Harry Potter did. Voldemort even more, to use a best-selling example. To be a bit more literary, Ahab is the fascinating character in Moby Dick, not good-natured Ishmael or the ebullient Stubbs; so what draws me to antiheroes?
I think it has to do with a writer's or reader's personality. I'm an analytic, and I like my stuff real, A to B to C. I believe there is no such thing as an absolutely good or absolutely evil person, and thus fictional characters have to be an amalgam of conflicting urges and traits. I'm sure at least once in a while Saint Francis cussed out a novice, and even Hitler painted roses.
See, this is what writing a thriller with a serial killer/blackmailed cop set of main characters will do to you – now I'm trying to make the bad guy likable, and the good guy slightly repulsive.