1. Usually, a self claimed internet residing 'know it all' who claims to have the knowledge to flop what he/she perceives as a 'conspiracy theory' on its head. This is often a means for showing off. The complete opposite of a hardcore conspiracy theorist, debunkers usually have little common sense, little or no ability to connect the dots, no respect for common sense and call everything that that is outside their narrow a conspiracy theory. Since they profess to rely on hard evidence so much, this often seeps out of the domain of 'hard evidence', and they begin to fabricate so called 'truths' based primarily on jumping to conclusions and ad hominem attacks. Their favorite tactic is to try to 'get something out of the way' by attempting to embarrass their opponent and call it a done deal.
2. The other type of debunker consists of those who are anti-establishment and attempt to expose mainstream fraud and nonsense for what it is using logic, anecdotal evidence, and supplemental facts and figures. They are commonly insulted with the term 'conspiracy theorist' by those who wish to tarnish their reputations. Although still fallible, anti-establishment 'debunkers' commonly have less of an emotional stake in their arguments, as they have seen the light far more than their naive counterparts. Some do, however, take this too far and become truly raving lunatics.
As Joseph explained why psychiatry is not hard science, the debunker yelled "STOP WITH THE CONSPIRACY THEORIES ABOUT BIG PHARMA". However, it's not a conspiracy theory that most funding for psychiatric studies comes from big pharma, that they fund the ads in medical journals profusely, that they conduct their own studies on the drugs they push, that they have a much larger budget (and therefore much larger influence) than the FDA, that they fund APA conventions, and that it is not hard to skew data if you have so much power and are working in a poorly understood area.