So couple has child. Couple not married. DC gets double barrelled name. Or couple marry, couple double barrel their name (or just woman does) and DC get that name. What are DC supposed to do when they have DC? Quadruple barrel perhaps? It's madness. Personally I am also aginist the father's name being taken as the default, very sexist and patriarchal. IMHO girls should get the mother's name and boys the father's. That way no names die out.