Would it be easier to mine rings, or to mine the icy bodies that feed them? How about icy asteroids, comets, or craters on the moon?
Then there's the PR element. Which would be more likely to receive a huge public outcry against it: picking up ice from the dark side of the Moon and random asteroids nobody can see, or mining those rings that so many people find beautiful? Yes, the rings wrap around planets bigger than Earth, and it would therefore take a great deal of time and effort to put a dent into them, but it's somehow much easier to see a campaign to get ring-mining regulated in the name of "protecting the heritage of all mankind" or somesuch succeeding, compared to declaring a hidden crater with some ice to be an International Park.
Things change greatly if you have other things going on in space. As many have said, mining rings for water on Earth is a waste of money and effort, when you could just use desalination or other tricks to isolate not-so-fresh water closer to home. If you have space-mining operations or colonies already, ring-mining seems slightly less pointless, but at the same time, regulating ring-mining for PR reasons also seems more likely. Especially if someone already set up ice-miners on icy asteroids or moons.