With the Gillard government being consistently outgunned and just plain monstered in public debate, it has more cause than ever to regret the departure of former finance minister Lindsay Tanner, who was one of the few politicians with the ability and inclination to actually explain things to the electorate. His talents were on display again last night when he delivered the annual Walter Lippmann lecture in Melbourne. (No, not that Walter Lippmann — this one.)

Tanner’s theme was the economic benefits of immigration — not the narrow “arithmetic” sort, but the advantages that flow from greater ethnic and cultural diversity. Multiculturalism, as he put it, is not a matter of “moral vanity or middle-class indulgence”, but an economic necessity.

Tanner painted an unflattering picture of the Australia of John Howard’s treasured 1950s: largely monocultural, hierarchical, anti-intellectual and dominated by “the British army model of business management”. It’s a reminder that always seems necessary, given our tendency to romanticise the past. But without the diversity that immigration has brought, it’s hard to see how Australia could have adapted so well to the challenges of globalisation.

The big advantage comes from being exposed to different habits of thought, to people who see the world differently. Tanner offered what he described as a “killer quote” from John Stuart Mill:

“But the economical advantages of commerce are surpassed in importance by those of its effects which are intellectual and moral. It is hardly possible to overrate the value, in the present low state of human improvement, of placing human beings in contact with persons dissimilar to themselves, and with modes of thought and action unlike those with which they are familiar … [T]here is no nation which does not need to borrow from others …”.

I think this is absolutely right. But it struck me that the moral is broader than the one Tanner drew: that the danger is not just a stifling ethnic homogeneity, but groupthink in general.

Specifically, I thought about right-wing or free-market think tanks. It’s a topic that’s in the news particularly with the now-resolved battle for control of the Cato Institute, but we have examples in Australia as well.

In the 1960s and 1970s, those who opposed the prevailing welfarist-Keynesian consensus, feeling shut out from influence in universities and policymaking bodies, established a variety of think tanks to hone and propagate their ideas. They became a rich source of innovative policy suggestions, many of which have been adopted by governments worldwide. Even those who disagreed with them came to respect their contribution to public debate.

But gradually, over the past 20 years or so, the think tank well has dried up. With rare exceptions, the output from those think tanks now seems querulous, repetitive, obscurantist. Their ideas and their thinking have become stale — the jihad against climate science is perhaps the most obvious symptom.

The problem, it seems to me, is that the think tanks sealed themselves off from diversity. Without disagreement, progress is impossible to sustain. Instead of getting jobs in academia and talking to those who came from different intellectual traditions, bright young graduates went into think tanks and just talked to one another. Groupthink took the place of learning; polemics took the place of inquiry.

The resulting ideas deficit has flowed through to the political parties of the right. They have convinced themselves that their opponents have nothing to say, so they feel no obligation to listen or to engage. The lack of any culture of internal debate just makes matters worse.

Tanner’s lesson on the benefits of diversity deserves a hearing beyond just the immigration debate.