Knowledge and Experience – or Imagination?

Well known, and in many ways brilliant, writer Anthony Horowitz has been warned off including black characters in a new book because an (American?) editor said it was inappropriate for a ‘white’ writer to create a ‘black’ character. He made the rejoinder that if you followed that train of thought he could only write about ‘62 year old, white, Jewish men living in North London’
What was that editor thinking?
A writer’s job is:
To tell a story by creating characters and leading the reader through the development of the plot by showing interactions between those characters.
I suggest that stories, characters and interactions would be incredibly feeble and tedious if all characters were a reflection of the writer.
That editor does not appear to allow for the one critical factor – imagination. Why is it artificial or condescending or patronising to include characters of different ages, genders, races and even sexual proclivities just because the writer has not had that personal experience? And in any case, are people so defined by their colour, as this editor implies, that empathy and understanding are impossible between different ‘categories’ (my quotes) of people?
For the past few months I have been writing my next murder mystery novel – Hostage to Fortune (hopefully out early 2018).
The story involves murder and abduction but I am neither a murderer nor an abductor so I presume to be able to put myself in the place of one who is.
Instead of knowledge and direct experience I have imagined; I have put myself in the position of someone in a certain situation and imagined what they would do and how they would act. This is what writers (good, bad and indifferent) do.
How many people did Agatha Christie poison, stab, shoot or otherwise do away with? How could she, as a well off, middle-aged, English woman possibly write about a pedantic Belgian male detective, an ex-policeman, refugee from war-torn Belgium, possible spy for the British, lover of steam trains, unlucky in love. Could it have been that she had imagination?
I could not have written any of my books including only white, thoroughly middle class, university educated, four times married, women in their sixties.
My characters are first and foremost individuals.
Ryan, Guy, Arjun, Luis, Barford, Pat, Diane, Skye and Fergal each acts and reacts in his or her own individual way, they have characteristics of their own, they have taken on lives of their own with individual motives and back-stories.
Ryan is immature, Guy is manipulative, Arjun is vulnerable, both Luis and Barford make mistakes though both survive them, both Pat and Diane keep too many secrets to themselves, and neither Skye nor Fergal can keep to their remit; but, when it comes down to it, their gender, sexuality, colour and age are probably immaterial to the plot but their differences make it, to my mind, far more credible.
In these days of inclusivity and diversity a book that contains characters who are uniform in gender, sexuality, colour and age would be completely improbable so, should that editor’s approach be accepted widely, every work of fiction would have to have multiple writers, each concentrating on their own insular and insulated little world, limited by their experience.
As a certain, brilliant, scientist (Albert Einstein) is quoted as saying “I am enough of the artist to draw freely upon my imagination. Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.”