Both Brexit supporters and Remainers can learn from what Professor Sims has written: both will find things in it which they like and things which challenge them (and if you don't you have not read it carefully enough.)
It is not very often these days which you read anything which seems to display an empathic understanding of all three of the viewpoints of mainland Britain, Northern Irish and Ireland (26 counties)
In his article,
"From backdoor to backstop: Ireland’s shifting relationship with Britain and Europe."
Professor Simms sets out how since the Middle Ages, successive governments of first England and then Britain have been concerned to prevent Ireland (and indeed Scotland and Wales) being used as a backdoor invasion route against these islands from both hostile European powers and indigenous rebels and pretenders.
If this makes it sound as though he is criticising England or Britain for this, the article didn't come over to me as ignoring English and British concerns. That's because Brendan Simms also points out that they had good reason for those concerns, and he records some of the rebels and European powers who over the last few centuries have threatened or indeed attempted exactly that strategy.
I might add that as some of the foreign regimes involved in those plots, strategies and invasions are still rightly remembered even today both for aggression against all their neighbours and for purges and mass executions against people they didn't like, from burning alive those with the wrong religious views to industrial-scale use of the guillotine against people of the wrong social class or political views, it would have been surprising if any English or British government had not taken action to defend itself and its' people against such attacks. You don't have to excuse or justify for a moment all the actions which have taken place in consequence to recognise this.
I would very strongly advise anyone with an open mind and an interest in either British-Irish relations or the future relationship between Britain and Europe (including whether and how Brexit happens) to read this New Statesman article, which you can do here.