The problem is that the basic story is now inherently "tainted" by the Disney version. It SHOULD be allowed to be a dark, scary tale, but no matter what, even if they made it R---there'd be 50 million parents who'd take their 4-year-olds to it just because they think "Alice=Disney", then loudly publically complain how scary a "kid's" movie was---it'd be on every news report how you shouldn't take families to see it.
Just like Jurassic Park. It was PG-13 for a reason. Dinosaurs are not inherently kid-friendly. They eat people. Messily. But parents still brought their kids because "kids love dinosaurs", then were horrified when they saw what the movie was actually about.
PS---story that suffers the most from having a famous, kid-friendly movie? The Tin Woodsman. Yes, the Wizard of Oz one. Try to find the real, original stories of him. Very sad when it's all said and done.