What makes Don Draper dashing is the suit, especially. And the hat, the jaw, the hair, the voice, the way he fixes his attention on a woman. But what makes Don Draper seductive as a person and not just a sexual partner is that he is perpetually a whisper away from being a better man. If he were just dashing, he would be harmless; it's that he's seductive that makes him dangerous. It's how close he seems to becoming better that makes him toxic.