So even the wildest wilderness can be heavily stressed by people and just little additional disturbance there can top the balance against the birds. Behaviour of tourism and ecotourism companies or guides is generally under the big pressure to snatch customers from competition on the rather small market. It is also rarely effectively controlled. Usually this was not because the birds were impossible to see otherwise, but because guides preferred to cut short the waiting time, get close-up photographic opportunities for customers, or didn't bother to visit the alternative site further from the road. If you are customer of such enterprise, don't assume that guide or organiser takes all responsibity for bird welfare.
Bad behaviour harms other visitors, too.
Access gets prohibited, birding information is withdrawed, or simply annoyed local shouts abuse on tourists, often not the ones which made problems. Every case of unethical behaviour is also very damaging to the public image of birdwatchers. Such accidents easily draw the attention, even if less visible threats can be more important. Of course, wildlife is threatened by tourism everywhere in the world, from Minsmere to Mount Everest. I further believe that birding community can effectively, voluntarily control itself and keep the damage and disturbance to the nature to the minimum.