Actually, I think this also begs the question of if all professional assassins are inherently bad people. After all, isn’t Bond a professional assassin? Is he a bad person?
Oh my god, yes. Bond is such a terrible person. I mean look at him. He has just about every vice in the book, terrible impulse control when it comes to his personal life, he’s a misogynist (yeah, he’s good with Moneypenny, but the mark of a misogynist is not in the exceptions to the way he treats most women), he’s got a warped sense of the value of life in general, including his own. He has contempt for his own chain of command and yet he still follows it. Those are just the things I remember off the top of my head.
He’s a great example, really, of how a story biases us in favor of the main character. Despite all that being demonstratively true, we find it in ourselves to like him because we’re shown his inner struggles and how he comes to the decisions and behaviors he does. But the truth is, just because we understand and can sympathize doesn’t necessarily justify him making those choices.
I don’t know that Bond started out as fucked up as he is when we meet him. But truly, truly, killing people for a living—because it’s your job, because someone else told you to, maybe because you’re paid to do so—it does things to you. It does things even to soldiers, who are indoctrinated with the moral justifications of killing to defend their country, themselves and their allies, and are (at least theoretically) killing people who are trying to kill them back.
Check out the the literature; for most people, repeated killing creates lasting feelings of guilt, sometimes even PTSD. It can warp and devalue your sense of the value of life and lead you to a dehumanized view of others. In the long term, a lot of these people who do jobs like Bond does for a living, it hollows them out. They go numb, emotionally, stop connecting and empathizing with people, almost like it turns them into psychopaths. The way Bond is portrayed in the new set of movies is pretty well in-line, really.
Ian Fleming even talked about this himself, a couple of times: that Bond is based on people he knew who worked in Intelligence, and what they were like, and how stone-cold and frankly unpleasant the job tended to make them. Bond has a congenial demeanor when he wants it, and he’s not out of control (usually). But you can also feel him hollowing out, detaching and caring less and less as he goes through the story.
I can well imagine that Mary went through a similar thing. Maybe she started out as a really nice person—but there’s little possibility, especially given the cold ruthlessness we see her deploy, she could have simply stayed that way and remained untainted by a job like that. (And that’s not even touching on CAM’s sly little comment about her “going a bit freelance.”)
There might, in reality, be nice professional assassins. But just consider what you would have to do to your own head in order to justify to yourself the habitual killing—not just one, but over and over and over again—of people you don’t really personally know and have nothing personal against. Anyone who came to the job not already a psychopath would have had to do the same thing.