Denialists never want to admit that they are wrong about anything, so they keep a debate going as long as possible to sooth their egos. Then, when their views are discredited by the mainstream scientific communities, they appeal to the prejudices of the general public instead.

Global Warming (GW) denialist stages:

1. "Global warming is not happening and may not happen. Why worry about it?"
2. "Global warming IS happening, but there is no evidence that humans are a factor in the problem."
3. "Global warming is happening, humans are a factor, but there is nothing we can do to stop it anyway."
4. 'Global warming is happening, humans are a factor, we can stop it, but the costs of trying to stop it would outweigh the benefits."

Decades ago, most GW denialists were at stage one. Today, most of them are at stage two, with some already moving to stage three or four. Truly honest and fair people should have stopped at stage one.

Creationist (evolution denialist) stages:

1. "Species are eternal and unchanging, existing in their present form since Creation. There is no evidence for evolution."
2. "Species do change, but only within the limits of created kinds. Evidence cited for evolution can also fit within Creationism."
3. "Even if evolution occurs, an Intelligent Designer must have been involved, so complex are some biological forms."
4. "Evolution is as unscientific as Creationism."

The difference between a skeptic and a denialist, on any subject, is that a real skeptic knows in advance what evidence would convince him that something is real or that action of a certain kind is justified. A denialist has no such standards. His commitment to an ideology trumps any scientific standard. Gaps in scientific knowledge, which would motivate most scientists to look for more data, are wrongly used by denialists to reject completely a concept they do not like because of prejudice. This is dishonesty.