The multi-ethnicisation of Ireland over the past 20 years has been one of the biggest social changes ever experienced on this island. As recently as the early 1990s there were just 40,000 people living in the State who had not been born here, in Britain or the US.

At the time of the last census, in 2011, there were 199 nationalities - representing almost every country on the planet - making their home here. Today, a larger share of the population is non-national than the European average - and that change has happened at least as rapidly as in any other European country in living memory.

Despite the scale and speed of the change, it has taken place with far less friction than most other European countries.

A continent-wide Eurobarometer opinion poll, taken in June this year, found that just one in 10 Irish respondents thought immigration was the most important issue facing the country (five other issues, all economy-related, were adjudged more important). That was the third-lowest level among the 28 countries surveyed and less than half the average across the continent.

In Britain by contrast, nearly three out of 10 people put immigration as their biggest concern in the same poll. That is despite a proportionately lower numbers of foreigners living there compared to here and the rate of joblessness standing at half Ireland's rate.

That the issue is less salient than many other issues for Irish voters is reflected in politics and society. Immigration has hardly registered on the political Richter scale in terms of deciding votes, and the kind of events that took place in Waterford last weekend have been few.

Even a depression-scale economic crash did not trigger a visible change. No anti-immigration party came into being and the traditional political parties have not sought to win votes by out-bidding each other on proposals to curb the numbers of newcomers. This is exceptional in western Europe today.

Why is Ireland so unusual?

It could be that having experienced so many generations of exporting our young, and having come to see how that drained national vitality, we now see the arrival of people in the prime of their working lives with education and skills (unpaid for by Irish taxpayers) as a windfall for the country.

That, in fact, would be a very rational conclusion. Evidence from Ireland and elsewhere suggests that immigration tends to make countries stronger economically.

But no serious observer would claim that any phenomenon as big and as complex as immigration is without downside.

One potentially negative aspect is the effect on the lower paid. Immigrants tend to be better represented in the lower half of the income distribution. This puts downwards pressure on pay rates and can contribute to a widening of income inequality.

Immigration can also destabilise economies if it happens too quickly. With the benefit of hindsight, it seems clear that the full opening of the labour market in 2004 to workers from 10 countries that joined the EU at the time fuelled the property and construction bubble. Many of the quarter of a million non-nationals who arrived in the three years to 2007 worked in the building industry. All needed roofs over their heads. Along with inflows of too much foreign capital, too much foreign labour caused the construction sector to become so bloated.

But it is the social, rather than the economic impact of immigration that raises the most troubling questions, because that dimension is less about benefits and costs and more about one's concept of what makes communal life good.

For what it is worth, my preference is and always has been to live in culturally-diverse settings, and that is one of the main reasons I've spent most of my adult life living in other countries. But many people prefer to live among those who share their points of reference - be that sport, politics or local history - and with whom there are no cultural or linguistic barriers.

One view is not morally superior to the other, and those of us who prefer diversity should be cautious about dismissing as racists those who are more comfortable with that which is familiar and similar.

Nor is diversity without downside. Robert Putnam is one of the world's big thinkers on the cohesiveness of societies and their "social capital", a term to describe the intangible strength of societies whose citizens are willing to help each other and do things in the common good, such as join charities and volunteer time to sports organisations.

Putnam has found that the more diverse societies become, the lower their social capital. In other words, the more people differ from their neighbours, the less willing they are to be involved with them and help them.

This is to be seen in societies as historically open, accepting of difference and tolerant as the Netherlands. Its political and social discourse has changed a lot as views on immigration have hardened since the turn of the century. The same can be said for the Nordic counties. All of these countries now have significant anti-immigration parties, all of which are populist if not reactionary.

The issue of immigration throws up hard questions for the media. In Ireland, there has been very little discussion of the phenomenon and almost no discussion of the downsides, unlike any other country I know (nothing illustrates this better than the differing content of the Irish and British editions of the Daily Mail newspaper).

This raises the question: to what extent do people become excessively fearful of the downsides of immigration because they hear a lot about the subject in the media? The answer could be: quite a lot.

Humans evolved to have a finely-developed sense of threat from outsiders and strangers. Although we now live in much-less dangerous societies than our forebears, we haven't lost that trait.

This was highlighted by an opinion poll taken in Australia, Britain, France, Germany, Italy and the US and published in the London Times last week. Pollsters asked people in each country to estimate the proportion of the population that is accounted for by immigrants. In all four European countries and the US, the average guess was far in excess of the actual number, ranging between twice and more than four times the real proportion.

It could very well be that the Irish media's lack of coverage of the phenomenon has made people more relaxed about the changes that have taken place.

But it is always risky to brush things under the carpet. The attack on the home of a Roma family in Waterford city last weekend may have been an isolated incident, but it could also be that there is more disquiet about immigration bubbling beneath the surface than polls suggest. Not venting that disquiet could potentially lead to more of it building up and a less-controlled release in the future.

Talking more about immigration - its downsides as well as its upsides - would also make it more likely that there is a political focus on learning the (many) mistakes and missteps of other countries. Failing to proactively learn those lessons would be a serious failure and could mean that the kind of ugliness seen in Waterford last weekend becomes more common.

Sunday Independent