As someone who makes their living doing workshops and taking people to 'tourist attractions' and 'religiously significant' and 'culturally significant' sites I can emphasize with Mark's observations but I cannot agree with his conclusions.
1. I think it's presumptuous to judge how others enjoy art, and just plain wrong to dictate it. I'll admit when the tour buses air brakes signal the release of another bus load of loud and obnoxious Korean and/or Chinese tourists at Angkor Vat or the same at Wat Phra Kaew or any number of such places I cringe and resign myself to waiting out their departure while they shout, spit, and yell while in some cases physically climbing all over the artifacts. Indeed it's a "learning moment" for my students who by and large know better themselves, but observing the cultural aspects of behaviour might be new to them. The bottom line is these groups are enjoying themselves and paid the costs and endured the journey to get there just like I did. Their behaviour while a reflection of their culture, is also allowed by their hosts. There are better managed sites which demand and monitor acceptable behaviour so it can be done.
2. Protecting the site is mandatory and no where is this more evident than in South East Asia where many of the sites are centuries old and in different states of decay and/or restoration.
3. Photography. The flash problem is simple, do what most museums have been doing for decades.. restrict flash photography because it is destructive and distracting to others. If you must restrict photography to create a desired "feeling" then do sponsor frequent and helpful "photography access" to accommodate photographers. You won't find many cell phone snappers signing up.
4. The annoyance isn't with the type of camera. A DSLR or rangefinder camera user can be just as annoying as a iphone snapper. It's in the numbers, and of course with the behaviour and thoughtfulness of the photographer.
5. Times are changing. The first time I visited the Louvre there wasn't a McDonald's. Now there is. And judging by the throngs of hungry tourists waiting in line for their Big Mac it can't be such a bad thing. It's just change, and human animals resist and often deplores change.