He knows better.
This. The problem with O'Reilly isn't that he's stupid -- he's certainly no genius, but he's not a complete moron, either -- it's that he's willfully ignorant and not above intellectual dishonesty for the sake of stubbornness. He's perfectly capable of understanding why these arguments are idiotic, he's just too much of an arrogant, stubborn ass to shut the hell up and actually do the research, think things through, and
then form an opinion or, god forbid, admit that he was wrong about something. Instead, he hops on the bandwagon so he can have something to rant about.
Let's not give this guy an excuse for his bullshit by assuming he's merely stupid.