Any re-erection of barriers on island would be sheer madness
We are on the brink of abruptly changing the core policy of how the UK has been governed for the past four decades. Here in Northern Ireland, while the polls show a clear majority mindful of the real benefits for Northern Ireland of being inside, not outside, the EU, and in favour of staying, the two top people in authority - the First Minister and the Secretary of State - are actively campaigning to take the UK and Northern Ireland out.
If they succeed, will we see the reintroduction of a visible, physical border across the island?
There has long been a general consensus that Northern Ireland has done reasonably well in terms of grant aid and that being in the EU has helped economic recovery through, for example, inward investment and the growth of tourism.
Farmers have done well and, even though very hard hit at the moment, the weight of farm opinion would seem to be that current problems are more likely to be solved inside the EU, not outside.
The recent poll in the Belfast Telegraph showed strong public support for remaining.
How come, then, that the biggest party - the DUP - which has put economic recovery at the top of its agenda and has not been shy of stressing the benefits of Northern Ireland's position within the EU to potential foreign investors, how come it is now campaigning for Brexit?
I can't even guess at how the Secretary of State reconciles her responsibility to promote Northern Ireland's interests at Cabinet level with her strong support for Brexit.
Ms Villiers has repeatedly assured us that Brexit will not mean the reimposition of a physical, visible border in Ireland. She has not told us how we will manage that.
Norway and Switzerland have close ties to the EU and long experience of sharing borders with EU states, but both still find it necessary to maintain Custom posts and border checks with EU neighbours. Ms Villiers' fellow Brexiteer - former Chancellor of the Exchequer Nigel Lawson - has said he thinks border controls will be necessary. A cross-party committee of the House of Commons has concluded that imposing controls at the border would cause considerable disruption and suggested, as an alternative, strengthening the borders between the island of Ireland and Britain.
Even that outlandish idea - aimed mainly at controlling the flow of emigrants into the UK - would not solve the real problems that would arise with Brexit.
How, for instance, could cross-border shopping, subject to the tight limits imposed for bringing goods in from outside the EU, be regulated without checks at the border? What about the movement of farm animals back and forth? Could the heavy goods traffic by road continue uninterrupted? What about the increasing flow of overseas tourists coming here via the Republic?
At the very least, it would seem a whole plethora of new arrangements would have to be worked out - not by cosy chats between London and Dublin, but between the UK and the EU, for the border would be an EU one, rather than an Irish one. For more than two decades the island, in a very real sense, has been undivided. The border disappeared in 1993 when the Single European Market made Custom posts redundant.
We take it for granted that we travel freely all over the island, with no compulsory stops, queues, or formalities. Commercial traffic flows across what was the border with similar freedom. Little more than two decades ago you could see a queue of lorries a mile long awaiting clearance at Killeen. For the border to be reinstated in any form would be an enormous shock. Its practical impact on commerce, tourism and many forms of cross-border activity can only be guessed at, but would certainly be negative. The damage to public morale of such a backward step could be enormous.
It would be wrong to claim that the EU played a major role in bringing peace, of a sort, to Northern Ireland, but it has helped in rebuilding both community relations and the economy through financial aid and, more importantly, by providing a context in which antagonistic Irish and British nationalisms could see themselves as part of one greater and shared identity - the European one.
The shock of a re-erected physical border could be even more damaging symbolically than the as-yet-unmeasured impact on trade, tourism, and numerous other areas of growing north-south co-operation. It would say, very loudly, that we are going backwards, not forwards.
Dennis Kennedy was head of the European Commission in Belfast from 1985 to 1991