Scientific American has an interesting article, How to Convince Someone When Facts Fail. This blatant falsehood, "The 9/11 truthers focus on minutiae like the melting point of steel in the World Trade Center buildings that caused their collapse because they think the government lies and conducts `false flag' operations to create a New World Order," should lead the reader to carefully consider and evaluate what the article says.
I admit from my own personal experience, that when an assertion flies in the face of someone's world-view, it often creates such a revulsion that someone doesn't even want to look at it. It's very hard to push oneself over the hump and see what they actually say. The problem is that it goes both ways: anti-truthers reject off-hand that our government could have either helped 9/11 or committed 9/11, no matter what kind of evidence is presented. Many anti-creationist are just as ignorant about the science, and reject creationist arguments based on the world-view, rather than on understanding the science. I suspect that that is the case for anti-birthers, climate-change believers, and round-earthers.
Whenever I taught astronomy, or in general discuss the issue, I ask, what kind of personal evidence do you have that the earth is round? (There is plenty, if one can only notice.) (I might mention that at least one flat-earth theory is utterly darn-awful: it predicts literally no sunset and no sunrise; the sun is always above the earth.)
I assume that the author is unaware that United Airlines reported to the federal Bureau of Transportation Statistics (www.bts.gov) that UA175 took off at 8:23, and UA93 took off at 8:28. The 9/11 Commission and the National Transportation Safety Board claim that the takeoff times were 8:14 and 8:42.
Many anti-creationists are (or perhaps were, two decades earlier) unable to address correctly the argument that evolution violates the second law of thermodynamics.
I am unfamiliar, myself, with the birther arguments. One thing I know is that the most famous birther is Donald Trump, a con man.