Mab has an important job, keeping Outsiders on the other side of the Gate. The best way to do that is to be totally pragmatic and not let emotions sway her decisions. I don’t know about the rest of you, but I wouldn’t like to face an Outsider. Even one of the lesser ones (He Who Walks With His Foot Up My Behind??). Even Harry’s opinion of Mab has changed since he realized her purpose.