I thought she was really scary but I think seeing people be emotionally manipulated gets to me.Jasmine had all the trappings of the Anti-Christ. She was attractive. She would right long-standing wrongs. She consumed people but in a lesser quantity than the wars of the world. She would accrete power all to herself. For an avowed atheist, Joss had a very good representation of a true Anti-Christ, probably better than most Christians (who should know better). She was one of the most dangerous Big Bads because everyone (at least everyone else) aided and abetted her every move.
And let's face it - having the BMW driver stop cheerfully for a pedestrian? That takes some of the darkest mojo right there.