Is she though? Of course she's going to kill people, but how does that make her different from anyone excepting maybe Jon Snow right now? She can go one of two ways, I think. One, she goes crazy like her father and wipes everyone out, but two is that the whole benevolent side that Jorah keeps referencing and pushing comes out and she only rains Dragonfire on people who deserve it like stupid Lannisters and Stannis Baratheon. I don't know how her story plays out in the books (yet), but as an observer of the show, she's far from the bad guy.
To me, it feels like even the most obvious bad guy, Joffrey, is evil but is evil mainly because he's a spoiled brat who had no upbringing that would rein him in before he became King. Would he have turned out that way anyway? Only Martin knows. Pretty much at the top of the nobility chart is Snow and the bottom is Joffrey and everyone in between is some kind of mix between bastard and nobleman/woman