They Don't Like Us
It may surprise some to know that many people in the National Park Service, state, regional, and local park systems, and conservation groups, have a distinct dislike for nature photographers. It’s little wonder, really. Most have a long list of true stories about people violating park rules for the sake of a photograph. Topping the list is the well known tale of a professional landscape photographer who, while leading a workshop, used fire as a photographic lighting technique that caused damage to Delicate Arch in Arches National Park and other formations in Canyonlands National Park. He was tracked down, charged, and later “pled guilty to seven misdemeanor charges for injuring/ defacing mineral resources in a national park, setting an unauthorized fire in a national park, lighting/using a fire that damaged or burned park resources, leaving a fire unextinguished on public lands, and aiding and abetting”, according to the National Park Service. While this is an extreme and flagrant case, there are countless others of more minor nature and notoriety. In Yellowstone, violations of park rules by people with cameras are so numerous that it is hard to spend any time there without witnessing some violation of rules or ethics. People often approach wildlife too closely, walk where they're not supposed to walk, and even feed the animals, all in spite of published park regulations. 
 
Ignorance is Bliss
Some violations of ethics and law are committed unknowingly. These cases usually involve someone who happens to own a camera, does not know much about a given place or its wildlife, and has perhaps seen too many episodes of the Croc Hunter or Jeff Corwin. While everyone should be responsible for knowing the rules of the places they visit, and perhaps for doing a little homework before they go, this is unlikely to happen. Unfortunately, park officials can’t gaze into a crystal ball and tell who knows what they are doing and who does not, so we are all subject to rules based on the lowest common denominator. It is simply a fact of life.
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Serious Photographers
Serious photographers do not simply wander into places and start taking pictures. They usually have some specific goals, know the rules, and have researched the place and its wildlife. The relatively few problems that involve these photographers have a cause very different than the one already discussed. Consciously or otherwise, the photographer put the importance of the photograph above the welfare of its subject, and in some cases, above the rule of law. This is usually not a calculated and deliberate act. After hours, days, or weeks are put into getting an image, we can become so focused on the goal that we think of little else. We push things a little too far in order to "get the shot" and avoid wasting all the time we have invested. It is hard to know when you are crossing the line if you are not thinking about the line in the first place. That is the point of this article. We nature photographers need to occasionally remind ourselves of our own values, and why we do what we do.
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The Majority
The vast majority of nature photographers have never caused a significant problem, and have never consciously thought that their images are more important than the welfare of our parks and wildlife. Most will report serious violations when they see them, and many are in fact avid conservationists. I suspect that most, though, have bumped into that ethical line a few times in pursuit of an image. What we do when that happens can make a big difference. As with any group, it only takes a few problems to give everyone a black eye. Given the circumstances, it is important for photographers as a group to hold themselves to a high standard. Each of us is an ambassador of our profession, avocation, or hobby.

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Additional Resource: The North American Nature Photographers Association "Principles of Ethical Field Practices".