The thing is, as an adult, you're usually better equipped to deal with the fact that you like things that are marketed at the other. I had a long chat with two of my (male) colleagues this morning about Marvel and DC comics and the films and computer games that are coming out of them.
Another colleague (female) thought it was hilarious, and said she'd never seen me as nerdy and laddish before.
I don't give a rat's arse how she sees me. I like comics. I'm happy liking comics.
Contrast that to children in KS1 being told that the things that they like are not acceptable - then you get upset and anxiety and confusion. When you back this up with this strange set of rules that dictate who should buy what things; then I think you've got the making of a big problem.
There is no problem with a girl liking princess stuff. There's a big problem when a child, boy or girl, is told that they should not like princess stuff.