Tribalism in politics isn't always a bad thing.

I'm prompted to say this by the fact that at least one decent Leaver thinks May's Brexit strategy is wrong. Pete North calls it "unhinged lunacy" and a "clueless gamble."

Some of us, though, had an inkling of this months ago. This wasn't because we had greater powers of foresight. Instead, what strengthened my antipathy to Brexit was simply that many of the people who supported it were racists and charlatans. Of course, not all Leavers were by any means. And they had some good arguments, not least about the sclerotic nature of EU institutions. But the fact was that pretty much all racists favoured Brexit. For some of us, this set off the klaxons.

May is interpreting the leave vote as a vote against immigration because that's what it was for many of the noisiest Leavers. And for some of us, this was precisely the reason to vote remain.

I don't think that in thinking this way I was committing the "poisoning the well" fallacy. The fact that so many Brexiters were racists and buffoons was, to me, indicative of the sort of Brexit we'd get.

Instead, I was being tribal: I didn't want to be part of a tribe that had a disproportionate number of people I despised. I was using a form of the social proof rule of thumb. I was allowing the numbers of others making their choices to guide mine. The fact that decent people tended to favour remain (with of course counter-examples on both sides) strengthened by support for the cause.

Sometimes, this rule of thumb is good. For example, if you are in a strange city wondering where to eat, the fact that one restaurant is full whilst another is empty might well be a decent guide to their relative merits. In other cases, though, it can be dangerous: asset price bubbles can occur because of the mistaken belief that other people know what they're doing.

Social proof is an unreliable rule of thumb. What we have in this case, however, might be another example of how biases can cancel out. Had Pete, and other decent Leavers, used this rule of thumb in the way I did, it might have offset their wishful thinking - the belief that Brexit would turn out as they hoped. As Gerd Gigerenzer has shown, apparently irrational rules of thumb often lead to the right decisions (pdf).

My point here is of course not about Brexit at all but about the nature of decision-making. In a complex world, our individual rationality can be unreliable. To paraphrase Burke, rather than trade upon our own private stock of reason, we should sometimes avail ourselves of the general bank and capital of nations and of ages. When rid of the toxic assets of racism and dishonesty, that bank and capital told me to favour remain.