why is the novel so controversial?

Of course this novel should NOT be censored or banned. I can't think of any classic novels that should be. Frequently, censoring ideas defeats its own purpose. Scarlet Letter was, at one time, scene to be ant-Christian and lewd. Anything criticizing the church and dealing with sexual infidelity seemed to offend the very Victorian sensibilities in both Europe, and to a greater degree, the United States. The novel is simply a piece of historical fiction that serves to bring light to a part of human history. Our stories need to be told, read and heard. If we censor them, we build our society on lies and deceit.

oops, sorry Emily. I wrote about the wrong one. In the case of "Mice and Men" I suppose the controversy lies in the whole euthanasia element of the story. George shooting Lennie at the end might have been considered less than "moral", especially among religious conservatives. Interestingly many of the above arguments for the book Scarlet Letter are just as pertinent to Mice and Men.

you have help a lot for me because i didnt really get it. thank you very much :

You are very welcome!

It was controversial for being a demoralizing and violent novel, that is, a mercy killing ending. It also includes offensive language and racial themes. The plot also shows prejudice against some mentally disabled. You could read all the controversial quotes from the book on Booksontrial.com: https://booksontrial.com/controversial-of-mice-and-men-shocking-quotes/