The man shouting his denial regarding the holocaust is someone who has decided to take upon himself the judgement and cruelty of the public because he believes that they are being deceived and wants to give them information he thinks the people should have. In my experience, these people are sound in their logic, and it has been enlightening discussing these things with them. That's going into a conversation, not an argument, especially when you're not actually trying to do anything but be right. Keep in mind that group consensus is not the same thing as truth. Even if that group is the majority. even if that group includes the official narrative. Truth exists indifferent to majority and government support.
After all, this is the policy: "The one who wants to be deceived, let him be deceived."
The truth is out there, and the man standing on his soapbox feels that he has uncovered 'one of truth's protective layers' and he feels compelled to bring the truth to the people as he is aware that no one else is in any hurry to do so. That deserves respect, if you have noting nice to say, then say nothing. If you are able to challenge your previously held beliefs and biases, then hear him out with an open mind, then it comes down to logic, reason, and science. Hear a hypothesis, listen to the argument, and evaluate the evidence or lack thereof. If the hypothesis can be tested, test it. If an argument is logical, consider it. If evidence supports the logical argument, judge accordingly.
Ultimately, declaring that anyone is a "psycho" because they are saying something that you disagree with, makes you the "psycho". As a Psychopath is in capable of empathy and is disinterested, even disgusted, in the opinions and beliefs of others and will dismiss them without a second thought. whereas, the man on the street cares about the truth, cares whether or not people know the truth, believes that people deserve the truth and is willing to deal with "psychos" who will be disgusted with him and treat him like garbage for attempting to speak the truth, all for the benefit of others.
Regardless of what the subject may be, though the Holocaust is a prime example. A solid argument has been made against it. it's worth considering with an open mind, if for no reason other than to form a solid counter argument whenever the topic comes up. you can only form a counter argument by listening to the initial argument tho.