You make an excellent point. This is something all humans are subject to, not just NWBO believers, long or short... it's called confirmation bias.
It's very hard to counter. The funny thing is, it's even stronger in intelligent people who will work harder to research, and thus create even more confirmation bias. Their intelligence, research, and detail just reinforces that they must be right.
This is why clinical trials like the current NWBO trial are double blinded. Even though conducted by research scientists, PhDs and MDs, they are still subject to confirmation bias. They are emotionally motivated to see the results that confirm their biases, just like traders.
Emotion adds greatly to this, and what is more emotional than money and fear of losing, or fear of missing out on winning?