I've had a lot of experience with schools banning a dependency of something rather than the thing itself, allegedly because they feel that gives them more time to prevent it. If they can take a camera away before students start sexting, then the student never will have started sexting. If they wait until the student starts, then it actually happened.

Of course, that means also banning all the legitimate uses of cameras, implying that the school thinks students' primary use of cameras is sexting, which I find obscenely offensive.