Interesting that only half know Louis L'Amour and Zane Grey's genre. I've known those since I was a kid, though a rural South Dakota upbringing will do that I guess.
Although one wonders if War and Peace would have been as highly acclaimed as it was, had it been published under its original title War, What Is It Good For.
Insert the standard, "it's an American website with questions written in English. Hard to believe that it caters to primarily Americans, You're free to create your own". That said there my initial count has 9 questions based on American authors and 10 from the British Isles. Seems too anglocentric to me.
I would argue about watership down being a children's novel. I first read it in my forties. Very interesting allegory although I understand the story was derived from tales the author told his children
For one, Whitman is believed to have been either gay or bisexual based on his poetry, which is of course controversial for some. People have also criticized him for personal beliefs and possibly having relationships with boys. That's just what I found based in a quick search.
What's controversial about Whitman? I have the impression that he's universally both loved and revered.