It's an interesting point. Obviously, we don't believe that the Earth is flat. But how are we not succumbing to Semmelweis reflex ourselves?
Each example above plays out differently.
Flat Earth Theory - This one is the easiest. We can reasonably verify that the Earth is round without examining it from a far distance.
Moon Landing Conspiracy Theory - the conspiracists use observation in light of physical laws to make their position, just like scientists, but their analysis is very shallow. Here's a common example:
Science tells us that there's no wind on the moon. But, look at the photo below: we can clearly see that the US flag on the moon is "waving" in the breeze. Therefore, according to science, it must be fake!
https://s3-us-west-1.amazonaws.com/h...moon_flag1.jpg
It's true, there's essentially no wind on the moon (except that created by the Lunar Module). So how is the flag waving? Is it a conspiracy? When we analyze the flag photo more closely, we can see that there's a top support bar holding it in place. The flag is crinkled because it was folded up to conserve precious space in transit, not because it's waving in the breeze.
https://s3-us-west-1.amazonaws.com/h...moon_flag2.jpg
In fact, we know that properly flying the flag on the moon was VERY important, but difficult, so NASA engineers came up with a purpose-specific Lunar Flag Assembly Kit:
https://s3-us-west-1.amazonaws.com/h...moon_flag3.gif
In fact, for the second moon landing, Apollo 12, the astronauts couldn't get the horizontal pole to latch correctly, and the flag just dangled like this:
https://s3-us-west-1.amazonaws.com/h...moon_flag4.jpg
Dorothy Martin UFO Cult - Interestingly, analyzing this one is a little tougher. After all, don't we intervene in and "save" other less-intelligent animal species when their habitat is being destroyed? The universe is vast; it's reasonable to guess that it contains other intelligent life, and that such life would both be able to predict a world-ending catastrophe on Earth, and would want to intervene to preserve our civilization. In this case, our best bet is to apply the concept of "Extraordinary claims require extraordinary evidence." Martin's claim was extraordinary, but her evidence was very skimpy.
Similarly, "We landed on the moon" is an extraordinary claim. But, the
third party evidence for Apollo Moon landings is also extraordinary, so it's reasonable to believe the claim.
This is the difference between pseudoscience (fake use of science), and simply saying "We don't know."
So, cybersam, in that regard, yes, I agree. The best answer is always "We don't know." In fact, some scientists believe that the true secrets of technology are indeed concealed from us. Not because corporations are "hiding free energy" or the government is concealing a pill that turns water into gasoline or similar such nonsense. The belief is simply that when revolutionary scientific discoveries occur, they're immediately and wrongfully dismissed, because of Semmelweis reflex.
More broadly, we can look at
Brain in a vat theory, which is an example of
Simulation hypothesis. This concept is commonly explored in popular culture, most notably with the movie
The Matrix. Brain in a vat theory proposes that our reality is simulated, and that everything that we think is real is just being fed to a brain sitting in a vat in a lab. We can't prove or disprove this theory, and we may never be able to do so.
