Why is chewing ice bad?

I was wondering, why is chewing ice bad? If ice is frozen WATER why is it not healthy to chew ice? I know it's a 'pica' it tells you that your body is lacking in iron but what I don't get is, ice is frozen water so what's the difference?

Chewing on ice cubes causes microscopic fractures on the enamel of your teeth, and also chips the ends of your teeth and most insurance companies won't pay to fix. And you are right chewing on ice is a symptom of iron deficiency anemia. Chewing on crushed ice doesn't cause too much damage. I have been chewing on crushed ice for years.

it can chip your teeth.