There's one view on the Brexit row that seems to me to be under-heard. It's that whilst Brexit might be (slightly) economically damaging, this is a price worth paying for increased national sovereignty and a closing of the democratic deficit. Such a view is of course questionable, but it seems to me at least tenable - certainly more so than some of the rubbish that's being spouted.

But we're not hearing it. Instead, outers seem to think that Brexit would both make us better off and increase national self-determination. The converse is true for most of the inners: they too seem to feel no conflict between the various values involved.

This failure to acknowledge conflicts between values is, of course, not confined to the Brexit debate. Very few of those who support immigration controls do so because they believe social cohesion is worth having at the expense of some liberty and prosperity - or at least they don't feel those costs as a deprivation. Similarly, right libertarians deny that equality is a value, rather than believe it is a value worth sacrificing for liberty and prosperity. And leftists don't see that a living wage or higher corporate taxes might cost jobs.

What we see in all these cases is a denial of Isaiah Berlin's claim (pdf) that values conflict:

The notion of the perfect whole, the ultimate solution, in which all good things coexist, seems to me to be not merely unattainable - that is a truism - but conceptually incoherent; I do not know what is meant by a harmony of this kind. Some among the Great Goods cannot live together. That is a conceptual truth. We are doomed to choose, and every choice may entail an irreparable loss.

This poses the question: why is there such widespread failure to see Berlin's point?

A large part of the answer, I fear, is that partisans tend to be fanatics who overstate their case; not many of the protagonists in the Brexit debate take the - to me reasonable - view that the stakes are low.

You might think that in saying this I've fallen for a selection effect. We hear disproportionately from dogmatists and fanatics simply because TV and radio producers are more likely to invite them onto their shows than people with nuanced views who are troubled by trade-offs*.

But maybe something else is at work. It's that once you've persuaded yourself of the merits of an argument, three cognitive biases kick in to play down trade-offs:

- Asymmetric Bayesianism. We tend to be more sceptical about arguments from the opposing side than from our own, with the result that a balanced presentation of the evidence increases our dogmatism.

- Wishful thinking. For example, those who value national self-determination want to believe that Brexit will also make us better off - and wishes often beget beliefs.

- The halo effect. We tend to believe that good things go together, even though they needn't. For example, attractive defendants are more likely to be acquitted than ugly ones. David Leiser and Ronen Aroch have shown (pdf) that this characterizes lay people's thinking about economics. They show that non-economists apply a "good begets good heuristic": they tend to believe that good things lead to other good things.

Berlin went on to write that those who deny trade-offs rest on "comfortable beds of dogma". He should have added that such beds are easy to make.

* I'd like to hear interviewers ask: "what is the strongest argument your opponents are making?"