How is of mice and men controversial?

I need a list of reasons why. I have to do a presentation explaining the book, i already read it but i need specific reasons why it is controversial of banned at some place. I already tired looking on the Internet, but they don't have specific reason.How is of mice and men controversial?
It is controversial in the topic of mental illness, that of Lennie.








The following is a good link:





http://www.wset.com/news/stories/1207/48鈥?/a>





This has some value:





http://www.progressiveu.org/193941-shoul鈥?/a>