It can depend on the goldfish I guess. I only keep egg shaped fancy goldfish with long flowing fins, and I've read that these are more docile than commons or comets. That may play into it.
The really small "pest" snails that come into the tank on plant roots aren't really desirable IMO
, so it's good that goldfish would eat these.
You REALLY don't want your snails reproducing anyway, so you'd want your goldfish to eat the eggs. Hey it's free food!
I'm not sure how a goldfish could "tear a snail apart;" how would the goldfish get the hard shell open?
I'm also not sure how snails are "messy." What type of mess do they create? I've only observed areas of the tank with a lot of debries get cleared out by snails.