I'm probably in the minority, but I don't think I'd ever go to Disney as an adult with no kids. Don't get me wrong, I love taking my family and seeing the magic through their eyes. But when I see adults there on their own while I don't judge them, I do genuinely wonder why they come. Sure, it's fun and all, but if I was traveling without kids there's so many other options. Standing in line to greet a sweaty person in a costume when I could be relaxing on a Caribbean beach or strolling the markets of Provence?

But, hey, I don't see the point of boxing matches or country music concerts either but if that's your thing I would never say you shouldn't go.
One thing that I do object to, though, is any sort of "adult" behavior at Disney that detracts from the wholesome family atmosphere of Disney. If you want to get tipsy, use foul language, make out with your partner etc, then you should go to Vegas and have a "real" adult holiday. And you should expect strollers, energetic kids, excited teenagers, and lots of chaos that comes with vacationing families.
So, I have to agree with those who've said that Disney is for kids of all ages. I just have slightly higher standards for the behavior of the adult kids.