A conspiracy theory website I once read literally argued: Are you going to believe some "experts"?
It has always puzzled me how so many conspiracy theorists have managed to practically reverse the meaning of the word "expert", and have it mean someone who is not a reliable source of information, whose view on the subject is actually more suspect than that of the average person. And what's more worrying, many people have embraced this notion that "experts" are not be trusted on the very subject of their expertise.
To get a perspective on this matter, consider the following scenario:
You have a heart problem that requires surgery to be fixed. Now, who are you going to trust more to give you better advise on the problem and to operate on you, a professional cardiac surgeon with 20 years of experience on cardiac surgery and a phenomenal track record, or a random guy in a basement who has never even seen an exposed heart in live, much less operated on one?
Suppose that the expert cardiac surgeon, after studying your case extensively, highly recommends the surgery, and assures you that it's a routine surgery and there's a very good chance of success. The basement guy tells you that you don't need the surgery, and that it's all a hoax. He argues: What? Are you going to believe some "expert"?
Of course I'm going to believe the expert. No sane person in their right mind wouldn't. None of these conspiracy theorists would do otherwise either, if it was their health that was at stake.
So what's different when we are talking about conspiracy theories? Why are the experts in the related fields suddenly less reliable than some random guys in their basements who have never done any kind of research or work on those fields?
It's easy to doubt the experts when it's not your own wellbeing that's at stake. However, compromise it, and suddenly even the most hardcore conspiracy theorist will suddenly believe every single word an expert will tell him, if it will save his life.
On the same line, consider the following:
If you need the heart surgery to fix the problem, who would you trust more for opinions and to perform the operation, the expert cardiac surgeon with the 20-year impeccable track record, or a dermatologist with a 20-year impeccable track record in his field of expertise (ie. dermatology)?
The dermatologist may be a highly competent medical professional in his own field, and an absolutely trustworthy expert on that. However, that doesn't mean he knows anything about cardiac surgery. Just because he is a medical doctor doesn't mean he is an expert in all branches of medicine.
Clearly no sane person in their right mind would believe the word of a competent dermatologist over the word of a competent cardiac surgeon when discussing about heart surgery.
However, that's exactly what conspiracy theorists like to do. They will find a PhD that agrees with their conspiracy theory, and prominently quote his statements.
Of course when you are presented with the claim that some PhD agrees with the conspiracy theory, the very first question that should come to your mind is "PhD in what"?
In the same way that medical doctors are not experts in all fields of medicine, PhDs are not experts in all fields either. A PhD in mathematics may have no relevant expertise in biology, for instance. Just because someone has the title "PhD" doesn't mean he's a reliable expert. (In fact, the title of "doctor of philosophy" in relation to science is even less telling than "doctor of medicine" in relation to medicine because science in general is way, way more varied than medicine, with fields that have absolutely nothing to do with each other.)
If, for example, the subject is, say, the theory of evolution, you should consult a PhD in biology. The word of a PhD in mathematics or a PhD in English literature is as worthless as that of an average person on the street. (It's even less worthy than the word of a dermatologist on the subject of cardiac surgery, yet you wouldn't trust him fully in this case either.)