Or, to put it another way, imagine two conversations that make my point.
Here's the first one:
Teetotaler: Hey there, buddy, I think you've got a drinking problem.
Casual Drinker: No I don't. I have a glass of wine with dinner occasionally, and sometimes we have a couple of beers on Poker Night, but other than--
Teetotaler: DENIAL!!
Casual Drinker: What?!?
Teetotaler: Denial is a sure sign of alcoholism! You're an alcoholic!
Casual Drinker: But, wouldn't someone who doesn't have a problem also say that they don't have a problem?
Teetotaler: ...well... everyone who drinks has a problem.
And the second:
Global Warming Denialist: Global Warming is a left wing plot to destroy the world's economy, plunge us into chaos, and make everyone wear hemp jeans and Birkenstocks. The worldwide community of scientists and the evil liberal media are conspiring with Al Gore and that evil crying Native American from those 1970's anti-pollution ads, in order to attack capitalism!!
Normal Person: Yeah, but... isn't that a little bit silly? No one would really act that way, and scientists working in labs have little to gain by just making stuff up. Frankly, the whole thing sounds like a nutty conspiracy theory, just like the 9/11 Twoofers, the JFK assassination weirdos, the UFO--
GW Denialist: HAH! You're part of the conspiracy! You hate America!
Normal Person: What?
GW Denialist: See, you've been corrupted by the conspiracy, the lies of the media and the hippies and the commies and the PC police and the other varied forces aligned against democracy and freedom!!
Ok, maybe that was a little exaggerated? But, it does bring up a good point: for some people, evidence presented for their claim is proof of their claim... and evidence against their claim is also proof of their claim, because it proves that there really is a conspiracy trying to suppress their "truth."