Sorry, you're right, I was a bit... hyperbolic. You can drink it every day without problems since 1) it's not as pure as we like to think it is and 2) you can easily get all your minerals and stuff from your food.
The danger is if you decide to chug a bunch of water for one reason or another. It's easier to give yourself water intoxication with distilled water, essentially because the osmotic pressure is so much higher relative to the inside of your cells. This isn't actually a problem most people have to worry about, water intoxication is pretty rare, but I'm used to thinking in terms of hardcore athletes. It would be foolish to drink only distilled water for a marathon, for example.
Plus disabled people, plus people in an abusive relationship, plus depressed people, plus people who are just plain gross. Who wouldn't want to live in a world where all these people have better teeth?