Would you have felt the same way if they were total strangers? Why should two people who are traveling together not choose their preferred seats if they are available? How are you harmed more than if they were strangers? Why is this a moral issue? Maybe they weren't married. I often travel with a family member. He prefers window; I prefer aisle. If there is a window and an aisle in the same row, then we book them; if not we'll book windows and aisles in other rows.