Imagine you go to the doctor for a check-up. During the visit, the doctor mentions that they recently purchased a new diagnostic breathalyzer tool that can analyze the concentration of a particular compound in your breath and accurately diagnose if you have various cancers.
You agree to be tested, and after analyzing the results in the adjacent room, the doctor comes back into the office completely pale and accompanied by several emergency medical professionals wheeling a stretcher behind them.
"I am very sorry Mr. X, I am afraid that you have a severe growth in your body and require immediate surgery - possibly with the need to amputate one of your limbs!"
"What!" You say. "That is really horrible. what is the level of accuracy for this diagnostic test?"
The doctor gets a little uncomfortable and begins hemming and hawing.
"Actually the designers of this test have tested the device a whopping 108 billion times. Except for several instances, the device has incorrectly diagnosed cancer ALL 108 BILLION TIMES."
"Wait," you say. "I just want to make sure I understand. Are you telling me that every single time that this device has been used it has incorrectly diagnosed the existence of a tumor?! If so, why should it trust the accuracy of the device and have one of my limbs amputated based on its word?"
"Well," the doctor says, apparently prepared for your question. "Of all the other cases we have never seen numbers as high as yours. Sure we get lots of false positives, but your numbers seem off the charts. Your case is definitely accurate"
"Oh, by the way," the doctor says, "Once we found out about the growth we ran a number of other tests to confirm the presence of cancer. None of the other tests showed a positive result. According to them, you are perfectly healthy. However, despite the results of those tests I still must recommend that you have the surgery done based on the compelling results from the breathalyzer test."
Now I ask, in this situation, would you actually listen to the doctor and have your limb amputated, or would you get the hell out of that office?
This argument is insane, however, it is precisely the Kuzari argument. At its heart, the Kuzari argument is an appeal to the power of human incredulity. God must have appeared at Har Saini because such a lie is impossible to fabricate. People aren't that gullible to believe such an impossible story having not heard it from their own parents.
The argument essentially claims that the human "gullibility meter" would filter out this lie and not allow it to become accepted as truth.
But how accurate is the human gullibility meter - especially when it comes to religion?
The answer is that for as long as recorded history existed, we know that people have always believed utterly bizarre and silly ideas. This is certainly true from Judaism's perspective, which views with horror at the absurd religions floating around the world. For hundreds of years, people overcame their parental instincts to burn their children before Molech. What was their evidence that Molach existed? What 'outsider test of faith' did they perform before sacrificing their child to their God? The answer is none. Like it or not, we are very gullible. If from the moment we entered the world, our parents and friends and the larger community all accepted an idea - no matter how absurd - as true, it is incredibly difficult to free our minds of that belief long enough to analyze it with a critical mind.
Another example, ask a Jew if Christianity is plausible. Just because some people claimed they saw an empty tomb, suddenly it is logical to believe that the Son of God died for our sins?! how can 2.2 billion people living in our modern world believe this nonsense?! or consider Islam. some illiterate nutcase claims the angel Gabrial appeared to him in a private meet 'n greet and before you know it, 1.8 billion Muslims are fasting for a full month every year. Insane! How is this possible?!
The answer is that our 'gullibility meter' is terrible. It is completely absurd to then turn around and use that very diagnostic tool to verify the veracity of our religion.
Given the history of human belief, the idea that "the people would never have believed such a crazy claim" is very silly. This insanity is compounded by the fact that there exists another tremendously effective method to verify the truth about reality, namely, the critical study of the world around us. That form of truth-seeking has proven itself as the most incredibly useful tool humans have ever created, giving us mastery over the entire planet. Yet when this study is pointed at the truth claims of our religion, it comes up with one clear and unambiguous conclusion - Judaism is false. Every testable claim that our religion makes that has been scrutinized by the unfeeling gaze of scientific analysis has been found lacking. (See this post for a list of a bunch of them: https://malimaalah.wixsite.com/offthederechthoughts/home/180-reasons-to-question-the-truth-of-judaism) A critical examination of the evidence has yielded a vision of reality that utterly contradicts the narrative believed for millennia by orthodox Judaism. Yet in the oddest display of irony, we are asked to suspend all logic and believe the unbelievable. Why, because there is no way our parents were so gullible to believe the crazy story of Matan Torah.