I think this example helps explain the process that a denialist goes through with the denialist's own ridiculous analysis. In the NGO's case, they took a relatively simple equation used to calculate the equilibrium result for climate change based on increased CO2, and applied it themselves, without seeming to care that all the established climatologists had totally different result. Unsurprisingly, they did it wrong.
It seems like a combination of incredible hubris, thinking they could do a simple thing right that everyone else had done wrong for some reason, and further thought, according to journalist Stephen Leahy, something like "well at least it will get a conversation going about this important issue." In other words, accuracy is less important than getting attention in the direction they want to see it go.
Straight denialist-like/skeptic-like motivations, with the exception of a few denialists who may be completely lying or utterly uninterested in the accuracy of their claims.
UPDATE: And of course, I personally would never take a simple argument, like tidal amplification, and claim to find a new effect that no one's ever noticed.