Well, it's hard to blame them for being skeptical of accepted views, given the amount of lies and half truths put out by government and corporations. In many of those examples you cited (economy and politics), the general consensus of those on these forums are quite right, as far as I can tell.
Certainly, it is in Big Pharma's interests to keep people medicated all the time, but from my experience, that doesn't really stop real work from being done. It makes technological stagnation profitable (companies get to continually ride old or near-worthless discoveries for decades by manipulating the system), but if a real cure is found and demonstrated, it would still make it through.
A certain degree of skepticism is healthy. Of course, many people here buy into every new conspiracy theory that comes along. I personally think that the only truly dangerous conspiracy out there is the banking conspiracy, although there is certainly collusion everywhere touched by government. My basic assumption, which may or may not be flawed, is that the vast majority of people do what they think is good for the vast majority of the time. If they get involved in something nasty, they are likely to blow the whistle. If the FDA were contaminating our food on purpose, it would come out. If there was a conspiracy to make the public stupid and complacent through use of fluoridation, it would come out. Et cetera. All it takes is time. If someone had "made up" the HIV virus, it would be VERY obvious. Indeed, since it was at a controversial theory at the time that it came out, it was put through the ringer, and stood up to all criticism. That's how science works. It's not just research-->hypothesis-->experiment-->observation-->confirmation/contradiction, but it includes more steps -->peer review-->criticism-->repetition of the experiment-->presentation of results-->questioning-->further refinement-->publication-->more questioning-->more experimentation-->more refinement, and so on until you have a pretty damn good idea of what's going on. This process includes dozens, hundreds, and often thousands of people, all with different agendas and conflicting interests. Much like open source, there are so many eyes on this research that it is very difficult to slip in falsified results or data. If it is important enough for someone else to read it, someone will almost always find the fraud, and when it comes out, that researchers career is over.
Because of this rigorous and open review, most science questions are pretty cut and dried by the time they reach the general public. There are always a few who refuse to be swayed by any logic or set of evidence, but they are almost always in such a situation due to the end result of a series of escalating investments to try to save face (coming up on the wrong side of an argument a few too many times and they start to think that everyone is out to get them, when it's really that their theories don't hold water). I think that is the case with most of these AIDS deniers. That, or they have a vested monetary interest and have thus convinced themselves that they are right, despite the preponderance of evidence.