Well we are all untitled to our own peeves. I just don't like it because as another person said EEs are a plan. Just like how people hate buffs for buff orps I hate mutt for EEs.
Being planned doesn't make a mixed breed not a mutt, though? I planned a few years ago to breed my Silkie rooster to one of my Cochin bantam hens and a couple Easter-egger hens, and the resulting offspring of those birds are still mutts.
Also, hatchery 'Americaunas' that are actually Easter-eggers... don't have a plan. They're just bred to each other. You could argue that things like Lakeshore Eggers and Whiting True Greens and the like 'have a plan' and are Easter-eggers, but not all Easter-eggers do. They just all fit a loose definition of a specific group of chickens that are not pure for any breed, otherwise known as being mutts.
But yes, you are entitled to hate calling them mutts, just as I am entitled to continue using it as a term that is, in its definition, accurate for them.