Orphan Black is about clones and conspiracies. Part of the series' appeal is doubtless its gimmick. The twinning process -- wherein an actor plays opposite himself -- has been around for decades, but Orphan Black does it better than almost anything before. Even when the clones hand each other glasses you forget special effects are involved!
I first heard the statement, "Once a cheater always a cheater" when I was in high school. Maybe some women are born with an innate desire to believe in the ability to change. I know I'm a little more evidence-based myself and if history is any indication, I'd say Don Draper will spend the rest of his fictional life appearing in the beds of women all over 1960s Manhattan.