People really hold on to the feeling of patriotism that the moon landing brought and this kind of comment ruins a lot of peoples (especially boomer-aged) world view. If the moon landing wasn't real then everything they have ever been told / believe in could also be fake. For me, 9-11 was that event, I was in heavy denial for years - even when evidence of stuff not adding up was shown to me, I could not accept it. But once I saw all the oddities about sandy hook - it opened the flood gates and finally allowed me to question many, many things.