Perhaps the people who throw the term around think it is justified by the use of the term deniers to describe people who ... um ... deny that human activity is contributing to climate change. They say it is objectionable to be compared to Holocaust deniers. What would they have prefered? Nay sayers? Sorry, can't havve scpetics. There are respectable people called sceptics and the people I label deniers use an entirely different methodology to genuine sceptics.
And that's the key. The similarity that justifies the comparison is in methodology, not morality (though therein lies another debate). Holocaust deniers refuse to accept evidence, apply inconsistent criteria, place absurd standards of proof on 'opposition' representatives and repeat tired, discredited arguments. They also have a flair for publicity and continually imply there is a vast conspiracy, funded by special interests.
That describes the so-called climate change 'sceptics' pretty well, doesn't it?
Where as Nazis liquidated their opposition in a ruthless genocide, based on intolerance, hatred, crazed ideas of racial superiority and total abrogation of personal responsibility.
That doesn't really describe the pro-AGW camp very well, does it?
So, to finish off, here is the final word on comparisons to the Third Reich, a bold two fingers to Godwin's Law:
Anthropogenic climate change is akin to the rise of Nazism.
CO2 = Hitler. Methane = Mussolini. El Nino/La Nina = Stalin (Shifty, untrustworthy, likely to change sides at any moment).
Appeasers and blind optimists are currently assuring us that CO2-Hitler is not warming the planet and will be content with his 1998 Anschluss.
And on a slightly more serious note, the rise of CO2-Hitler and his Thousand Year Reich, like the historical Holocaust, relies on the co-operation of an army of little Eichmanns (1). In the current climate (Boom! Boom!) that's us - unimportant drones toodling about our business, failing to take responsibility for our actions, trusting that the Powers-thatbe know what They are doing.
1 - 'Little Eichamnns,' wikipedia explanation of the meaning and origins of the phrase. Viewd 7th of December, 2009. (http://en.wikipedia.org/wiki/Little_Eichmanns)