I've long thought that the problem with politics isn't just what people believe but also the fanaticism and dogmatism with which they believe it. Tory attacks upon Mark Carney illustrate this fact.

Let's face it, these are motivated in large part not by the technicalities of monetary policy but by Carney's warnings before the referendum that Brexit would unsettle the economy. In this sense, they are part of the same mindset that demands that Remainers be lock up as traitors: they are an attempt to silence dissent. That's a symptom not just of the right's hatred of freedom, but of fanaticism and hysteria - of a belief in one's cause which is stronger than the evidence warrants.

But of course, fanaticism is not confined to the right. It can be found across the political spectrum - even, I suspect, among people who are sane and reasonable in other respects.

Which brings me to my problem - political institutions (including of course the media) select for fanatics. I'm thinking here of (at least) four different mechanisms:

- Fanatics are more likely to contribute a lot to pressure groups and parties, thus raising the salience of their pet beliefs. Anti-immigrationers have Migration Watch. Those of us sympathetic to open borders have no equivalently powerful organization, perhaps because we are less willing to pay big money for it.

- The BBC is more likely to invite partisans onto its discussion programmes rather than those who are more sensible or who see both sides. For example, we hear a lot from the Taxpayers Alliance relative to more sensible economists, and heard rather more from Farage during the Brexit campaign than from more reasonable Brexiters such as Andrew Lilico.

- Fanatics are more willing to lie to support their cause and - with the BBC being impartial between truth and lie - this gives them an edge.

- Fanatics are often articulate about their cause, because they have so much practice in repeating it and because it's easy to be fluent if you rarely use the word "but". Because people are apt to take overconfident people at their word, this gives them a plausibility they don't warrant.

If we had rational political institutions, these biases would go the opposite way: fanaticism would be selected against, not for.

For example, one virtue of demand-revealing referenda is that people must say how much they are willing to pay to back a cause. Although the law of large numbers makes it unlikely that people really would have to stump up, such a process forces people to ask: how much do I support this cause? And it would also bring proportion to debates. Imagine if, during the Brexit referendum Evan Davis had been able to ask (say) Farage: "OK, how much are you willing to pay to leave the EU?"

Also, good institutions of deliberative democracy would select against irrational and over-stated arguments, and in favour of more correct ones.

And a BBC that took seriously its mission to inform as well as entertain would banish fanatics from its airwaves in favour of reasonable people.

But of course, we are miles away from such institutions - which means that politics is disfigured by a hysteria we see in few other walks of life.