Most of the people who ask me that question are people who go to the same place year after year on their vacations - beach, moutians, Vegas, camping, golf, whatever. Once I point that out to them, they are still incredulous that I would want to go to WDW over and over again.
It's not that they can't understand wanting to go to the same place year after year, it's that they can't understand anyone wanting to go to WDW even once. Whether they think it's too expensive, or they think it's just for kids (thus torture for adults, like Chuck-E-Cheese), or they think of Disney as a huge, evil, heartless corporate conglomerate, they are predjudiced against WDW as a vacation destination for even one year, let alone every year.
Talking doesn't convince them. Some people will always look down on WDW fans.
I don't care what people think about me. I only care how they behave toward me, and as long as they refrain from asking loaded questions like, "Aren't you tired of that place yet?" (which insinuates that there must be something wrong with me for liking that place), I really couldn't give a tinkers damn about what they think of my personal choice in vacation destinations.