RE: Is having more than one cat in the city cruel?
I think that it is going to be a case of looking at it on a cat by cat basis. Some cats are obviously fond of each other and are much better together. Some cats hate each other and must for their own sakes be kept apart. Most cats it seems are happy to rub along ignoring each other.
I can sort of see something in the bit about urban cats feeling overwhelmed by other cat numbers, feeling unable to roam as far because of other cats they dont like. However I do not think restricting each home to a single cat is automatically the answer. Consideration should be given to leash use allowed cats to explore places that are maybe a distance from home. Also I do agree that open spaces are not necessarily favourites for cats - but providing cardboard boxes and tubes, some special cat shelves, maybe a tunnel through interior walls where possible can all help.