Really? Expell someone from the park for taking flash photos? Isn't that a bit of an over-reaction? You'd really advocate kicking dad out of the park for taking a flash photo of his kids on POC?
The vast majority of people who use flash on rides are, I think, simply wanting to take photos of things that delight or amaze them. Sometimes it doesn't even click with them that there's a flash until they take the photo. Sometimes it doesn't click with them that anyone else but their family is there because the other riders are hidden or in other cars. I don't think it's all conscious "me first" thinking. Some of it is just excitement and fun and thinking "OMG -- how cool is that?" And I'll bet its been happening as long as flash cameras have existed.
Enforcement is an issue too. I suppose you could interrupt the ride once or twice with voice-over warnings and then, if the flashes persist, stop the ride completely and pull the offending person off so that the rest of the riders can enjoy the remainder of the ride without flashes, but that would ruin it for everyone else too.
Also ... just because someone takes a lot of pictures on one ride doesn't mean that they are "adversely affecting the park experience for hundreds of people throughout their day". It may be only one ride, because it's a favorite or a favorite of someone who isn't there. Or ... could be that only one person complained while the rest of the ride didn't notice or didn't care.
It's easy to say "pull someone off and kick them out", but really difficult in enforce.