Eh, I've probably talked about this sometime before, but it's on my mind at the moment...conspiracy theories and fringe beliefs have a certain fascination for me, but going the other way: I'm aggressively skeptical of anything like that. Or at least I *think* I am - but wait a minute...
If I *did* harbor such a belief, would I be aware that it was one? I think so; it's not hard to know that almost everyone who's studied a particular issue disagrees with whatever the fringe belief is. But I'd also have powerful reasons to deny that fact to myself, to surround myself with only the voices of other true believers, to understate the consensus or overstate the degree to which there's any real controversy about the issue. If you think the HIV-AIDS link is a lie cooked up by the evil medical establishment and antiretroviral drugs are a sham, you can always find a hundred other people online with the same need to believe as you do, and together you'll work to come up with explanations that sound really plausible...to you, anyway. Maybe you're just ahead of the curve? Well, yes, that's a more pleasant thing to think. Hey, people have been ahead of the curve before, proven the establishment wrong before - maybe you're one of them in this instance. Some people are better at defending against this than others, but no one's as good at it as he or she thinks, and the most confident are often the ones who know the least (the Dunning-Kruger Effect).
What always strikes me about people who harbor fringe beliefs is that most of them *aren't* particularly weird or unreasonable otherwise. There's some tendency that way - people naturally drawn to fringe beliefs probably won't stop at just one or two - but when not talking about how 9/11 was an inside job or the earth is 6,000 years old, these folks are often as well-adjusted, knowledgeable and successful as anyone else. Which is kind of unsettling, but only in the way that any truth is unsettling: it might be far more comforting for skeptics to believe that everyone who holds a fringe or poorly defended belief is crazy or stupid through and through, but we do not have that luxury.
This does not mean, however, that when confronted with someone trying to convince me that the moon landings were faked, intellectual honesty requires me to give their opinions a full hearing or act as if there are two reasonable sides to the argument. We can't be expected to spend all our time refuting every crackpot idea we come across. But wherever I would draw this line is unavoidably arbitrary and self-serving: I have to decide which theories are crackpot and which are not, and I can't possibly do so without referring to what I already accept, nor can I be aware of or weed out every cognitive bias I have no matter how scrupulous I might be. And I'm as prone to wanting to be right as anyone else is.
Is there a point in here somewhere...oh, yeah: No matter how bizarre someone's beliefs or opinions are, we can't allow ourselves to disrespect them as people on that basis - we're all capable of believing bizarre things given enough internal and external motivation to do so. This doesn't mean the bizarre belief itself has to be respected, merely the humanity of the person who holds it. That sounds simple, but it's very, very difficult to do, in that people (myself included, I'm sure) identify themselves closely with their beliefs and opinions and will often take it personally if you tell them you think they've wandered off the reservation, even if you're as nice as possible about it. And it's just as difficult to bite your tongue when you're surrounded by what you're sure is nonsense, particularly if it's prejudiced or hurtful nonsense - not speaking up feels like you're condoning what's being said.
So we change the subject and move on, or register a light agree-to-disagree, to keep the peace. Sometimes it's just the best we can do. As a society, we can try to model and teach rationality and civility and hope that over time more and more people come to value and exercise it. That's evolution, though, not revolution.