why is lennies mental disability important?

essasy: 'You must state which book you have started reading. Attach a prediction to your statement about what human rights issue will be covered in your book. Explain why you believe this issue will be important in the story.'

So far i have: The human rights issues in 'Of Mice and Men' is that Lennie, a man with a mental disability, is treated poorly due to his mental disability. I think that this will be the main human rights because the stroys setting is during the Great Depression when there wasn't a lot of knowledge about mental disadility compared to what we know about it now. I think Lennies 'problem' is very important....

i cant explain why i think is issue will be important in the story, i keep drawing a blank. help? please and thank you? :)