For me, the line comes when you have a set of facts that utterly conflicts with what reason tells you. If you chose the ideological interpretation over the facts, then you have crossed into religion.
That's not necessarily bad. I'm a religious guy. When confronted with evidence that contradicts what the Bible tells me is true, that cannot otherwise be explained except as a direct contradiction between evidence and reason v. the Bible, I go with the Bible. That's why it's a religion. No, there's a difference between literal and non-literal. Believing the Bible doesn't mean I have to believe that Creation literally took 6 days. But wherever I have a conflict that is otherwise irreconcilable, I will absolutely go with my religion.
It only becomes a problem when you think you're religion is provable science. But no, I'm not talking about intelligent design (which makes a fine religious belief but is not science). I'm talking about former FCC Chair Michael Powell and the Church of the Libertarians.
You can read the details on my professional blog. http://www.wetmachine.com/item/596. Briefly, when Powell was Chair of the FCC, he wanted to deregulate the mass media, because Libertarian ideology says that all regulation is bad and that deregulation actually creates competition. Ever and always. To even think that regulation can create comeptition is a heresy to be abjured.
So Powell ordered a study done to determine whether there was any connection between ownership and local news. He had input into the study design. He could tell it contained no bias, and used valid information and valid assumptions.
The result was the exact opposite of what Libertarian theology predicts. It turns out that production of local news and information occured was inversely related to the level of local ownership. In other words, if you owned more media outlets, they produced less local news -- both individually and collectively (an exception fgor cross-ownership of newspaper and a television station in the same market, which had no impact either positively or negatively on production of local news).
There are several ways to react. One is to observe "hey, its one study in a complex market." The other is to say "sure, but why does federal policy assign a value to local news anyway?" The answer to that, as the studies authors explained, is because we have a good quantitative literature on the relationship between the quantity of news and the impact on self-governance. More news coverage = more incentive and ability of the public to exercise their political rights effectively. Reduce news flow and voter turnout drops and accountability drops.
Now the authors explain the results of the study using real economics, not ideological slogans you fit on bumper stickers or neat theoretical models which assume away the unpleasant factors. While one could build any number of theories to support a prediction that deregulation would produce more or less local news, the one that actually worked in the market is the one that predicted less news.
Powell's response was, according to FCC staff there at the time, to eliminate the study. Not just decline to publish it. Eliminate it. He gave orders to have every piece of paper associated with the report shreded.
That's not economics. That's religion. It is when the undeniable and unpleasant facts stare you in the face, and you chose to go with ideology and deny the facts rather than readjust your bias.
When we talk about getting the religious fanatics out of government, I worry less about Kevin Martin and his campaign to keep "the F-Word" off the air than I do about Michael Powell and his religious crusade to deregulate everything. CBS can afford to pay several hundred grand because Justin Timberlake showed off Janet Jackson's left tit. But we are all in big trouble when five comapanies control everything we see, hear and say.