As more people leave the church, more anti-BYU fans will be created. Not everyone that leaves the church becomes anti-BYU, but in my experience that has been the vast majority.
There is a little saying that my kids hear from Utah fans in elementary school: "BYU smells like pooh." My kids didn't know what to say so I told them to say "U of U stinks like pooh." Sometimes you've gotta match pooh with pooh.