Snagging as defined in the current BC freshwater sportfishing regulations synopsis: "snagging (foul hooking)… hooking a fish in any other part of its body other than the mouth. Attempting to snag fish of any species is prohibited. Any fish willfully or accidently snagged must be released immediately."
The way the regulations are currently written, if you are trying to hook a fish in the mouth, it is not snagging. There is not currently a rule which says the fish must bite your lure or bait. Until there is, I don't see any "grey area", flossing isn't violating any currently written rule. That doesn't mean it is ethical. That does mean it is legal.
The best way to get people to change the way they fish is to show them that your chosen method can be successful. People imitate success. I have met a couple people on the river this season that have said they started fishing for salmon on the Fraser, and this is their first year on the V/C. They literally don't know of another way to catch fish. Show them. Offer to share a bit of roe with them, or offer them a chum jig. Show them how to rig up.
I often offer to net or land fish for other anglers that appear new to the sport - rather than worrying that they are going to drag a foul hooked wild coho up on to the beach, I just assume they want to release the fish and make it happen. I'm sure I saved a Cultus lake sockeye and multiple wild coho by doing this earlier this season. I understand that it can be frustrating to fish around those who aren't doing it ethically, but if all the ethical anglers give up and move on, the situation will get worse, not better.