"what you like is for children, therefore bad"

Yes, I dislike this as well. Target demographics are mostly for marketing (unless it's early development educational media or something) and as writers like Philip Pullman said "I'm against anything, from age-ranging to pinking and blueing, whose effect is to shut the door in the face of children who might enjoy coming in. No publisher should announce on the cover of any book the sort of readers the book would prefer. Let the readers decide for themselves." Which could be applied to adult readers too.

What makes something adult, anyway? I often find "adult" media like Game of Thrones to have a more "immature" view of the world than all ages media. Often I wonder if these things are called "adult" because they paint a nihilistic, spiritbroken view of the world where nothing can ever fundamentally be better. Almost like a capitalist societies way of training people to accociate adulthood with compliance to an unjust and depressing system that cannot be challenged.