An aspiration to encompass more than news shouldn't mean a free for all. An ambition to reflect society in all its aspects shouldn't become an excuse for a cacophony of clashing tones and values. There must be a common intelligence and unity of voice. A serious paper does not have inevitably to be serious, but it must aspire to serious ethical standards, including fairness, accuracy and a willingness to correct its mistakes. Without these there can be no bond of trust between paper and reader.
Serious papers paint in the greys.
They know that they have some kind of duty to represent life in all its complexities. And serious papers recognise that they also have a duty to cover areas of life which otherwise would be neglected or ignored. That includes a duty towards serious theatre, art, literature and music. It means writing about such things as economics, foreign news, the environment and social policy. Seriousness doesn't mean purging your pages of all subject matter that might more naturally feel at home in a tabloid.