Being a self-perceived-intelligent pig-headed engineer myself, I think you're missing a critical component in that description. I'm right, until proven otherwise. Show me a trustworthy test, show me trustworthy data, show me trustworthy studies, show me proof from a respectable authority that I'm wrong and I will happily change my mind and apologize to you for wasting your time in having to convince me.
Not everybody seems capable of determing what sources are trustworthy and what sources are not. Combine the same self-perceived-intelligence and pig-headded-ness with a distrust of "government" or "the man", and there you have it. At that point, the "mainstream" "trustworthy" sources are just a part of the conspiracy, so the only sources to be trusted are those on the fringe that are supressed and bringing you the real truth.
I have a good friend who is a very smart autodidact, but also a massive skeptic. You could probably put him in the "holocaust denier" camp because of this. I've gotten into arguments with him about it a couple times, and the sources that he always brings up are aryan nation affiliated internet forums or postings on these forums linking to sources elsewhere. The main contention is the number of Jewish holocaust deaths. Of course, the sources that I cite to counter his arguments are all part of the Isreali Jewish conspiracy.