Why the Wild Things are Mean?

When I heard this book for the first time, I thought 'hmmm..I heard about it somewhere.. oh! the movie!' And time passed. I am easily distracted just like my daughter. And few weeks ago, I came across the article about Maurice Sendak, from New York Times. I still didn't think of reading his book. I thought it would come across again if I need to read. Few days ago, I was researching children's book list, and Where The Wild Things Are was one of the must-read. I realized it was time to check it out from the library.

Max dons his wolf suit in pursuit of some mischief & gets sent to bed without supper. Fortuitously, a forest grows in his room, allowing his wild rampage to continue unimpaired. The wild things--with mismatched parts & giant eyes--manage somehow to be scary-looking without ever really being scary; at times they're downright hilarious.

 --Excerpt from Where The Wild Things Are, Goodreads

My daughter was interested in the illustrations of Where The Wild Things Are. 
"Mom," she asked, "why do the wild things look scary and act mean?" 

"Hmm..," I hesitated and answered, " that's a good question. I need to think about it." 

Can anybody answer this question? Why the wild things are mean? Does every wild things are mean? Are they born like this? Do we stereotype on everything, everyone? Is it our mere perception? Hmm.. 

What is your opinion?