I started to write a post about arguments over principle versus arguments over numbers, but it turned into this screed about rigid thinking and free speech.
Now I'm going to start over and try to stick to the topic.
The vast majority of political debates center on principles. This is why such debates are pointless and infuriating. Let me explain.
In the engineering world, if we made decisions the same way political compromises are worked out, it would go something like this: Jim and Tim are designing an airplane and need to decide what kind of engine to use.
Jim: Propellers are the best choice. They have a long tradition, and have been used on many successful planes. In fact, every plane should have a propeller. When jets were introduced, it was a great disaster for the airlines. Didn't you see that a jetliner crashed last year and killed 200 people?
Tim: But propellers are old-fashioned. They're heavy and they could be a danger to people near the airplane. No airplane should have a propeller. People who like propellers are just afraid of change.
Jim: You know, Hitler loved jets. He wanted to use jet planes as a weapon against democracy. Are you against democracy?
Tim: No, you are probably against democracy because your propeller idea will destroy the country and leave us open to foreign domination. But I have a compromise to offer. Let's design a plane with a propeller engine on the left and a jet engine on the right!
Jim: That's an idea I can get behind. Plus, we'll have to have two totally different fuel systems, which will double the design work and ensure that we both have jobs here at the airplane company for a long time.
Of course, any company that designed airplanes this way would soon be out of business. In reality, the laws of thermodynamics -- the numbers -- essentially force you to choose the engine based on the plane's cruising speed.
If you think this is an exaggeration, I encourage you to read up on one case in which a flying machine really was designed this way. You'll find out that the Space Shuttle had such big, heavy wings because it was politically forced to do a secondary job (once-around reconnaissance missions) that is very, very different from its primary job of transporting things to and from orbit - a secondary job that it was in fact never used for. The CIA and Air Force were able to foist the big wings on the Shuttle because NASA needed their political support, even though the AF already had its own big orbital launcher...don't get me started.
Someone will argue that in politics, we don't have anything corresponding to thermodynamics. That is, there aren't any objective calculations that would help us make the best decisions. Books have been written debunking this claim. Just because we couldn't make exact calculations doesn't mean that some kind of quantitative reasoning would be a waste of time. We use inexact (sometimes really inexact) models all the time to design airplanes and they come out a lot better than if we'd just thrown darts at a list of choices.
But we never learn, maybe because deep down we like to argue, and if there's a rational basis for choosing, then we don't get to spew bile all over each other. The worst example inflicted on us has to do with immigration.
Because immigration policy is always argued in terms of principle and not numbers, you only ever hear two sides: open borders or closed borders. It doesn't take a Harvard Ph.D. to realize that the best level of immigration, however you define best, is somewhere in between the two. Our form of government forces a compromise, but it's a propellers-and-jet kind of compromise that satisfies nobody and makes no sense. The arguments are so soaked in principle that if you think there should be less immigration, you're called a racist, while if you think there should be more, you're called a traitor. It's like the guy on the freeway who thinks everyone slower than him is an idiot and everyone faster than him is a maniac.
Of course, both sides can and do refer to reams of statistics and projections to bolster their side. It puts a gloss of rationality on their argument, but that's all. They don't use data like they ought to. If you believe a study that shows a million immigrants a year are a net drag on the economy, then surely that same study could be used to determine how much fewer immigrants are the right number. 600,000? 300,000? But all you'll hear is that the study says there's too many immigrants. Conversely if a study says a million is too few, then the same study should say whether 1,200,000 is enough. But no, all you'll hear is that a study said we need more immigrants.